12 Aug, 2013
1 commit
-
commit 148519120c6d1f19ad53349683aeae9f228b0b8d upstream.
Revert commit 69a37bea (cpuidle: Quickly notice prediction failure for
repeat mode), because it has been identified as the source of a
significant performance regression in v3.8 and later as explained by
Jeremy Eder:We believe we've identified a particular commit to the cpuidle code
that seems to be impacting performance of variety of workloads.
The simplest way to reproduce is using netperf TCP_RR test, so
we're using that, on a pair of Sandy Bridge based servers. We also
have data from a large database setup where performance is also
measurably/positively impacted, though that test data isn't easily
share-able.Included below are test results from 3 test kernels:
kernel reverts
-----------------------------------------------------------
1) vanilla upstream (no reverts)2) perfteam2 reverts e11538d1f03914eb92af5a1a378375c05ae8520c
3) test reverts 69a37beabf1f0a6705c08e879bdd5d82ff6486c4
e11538d1f03914eb92af5a1a378375c05ae8520cIn summary, netperf TCP_RR numbers improve by approximately 4%
after reverting 69a37beabf1f0a6705c08e879bdd5d82ff6486c4. When
69a37beabf1f0a6705c08e879bdd5d82ff6486c4 is included, C0 residency
never seems to get above 40%. Taking that patch out gets C0 near
100% quite often, and performance increases.The below data are histograms representing the %c0 residency @
1-second sample rates (using turbostat), while under netperf test.- If you look at the first 4 histograms, you can see %c0 residency
almost entirely in the 30,40% bin.
- The last pair, which reverts 69a37beabf1f0a6705c08e879bdd5d82ff6486c4,
shows %c0 in the 80,90,100% bins.Below each kernel name are netperf TCP_RR trans/s numbers for the
particular kernel that can be disclosed publicly, comparing the 3
test kernels. We ran a 4th test with the vanilla kernel where
we've also set /dev/cpu_dma_latency=0 to show overall impact
boosting single-threaded TCP_RR performance over 11% above
baseline.3.10-rc2 vanilla RX + c0 lock (/dev/cpu_dma_latency=0):
TCP_RR trans/s 54323.78-----------------------------------------------------------
3.10-rc2 vanilla RX (no reverts)
TCP_RR trans/s 48192.47Receiver %c0
0.0000 - 10.0000 [ 1]: *
10.0000 - 20.0000 [ 0]:
20.0000 - 30.0000 [ 0]:
30.0000 - 40.0000 [ 59]:
***********************************************************
40.0000 - 50.0000 [ 1]: *
50.0000 - 60.0000 [ 0]:
60.0000 - 70.0000 [ 0]:
70.0000 - 80.0000 [ 0]:
80.0000 - 90.0000 [ 0]:
90.0000 - 100.0000 [ 0]:Sender %c0
0.0000 - 10.0000 [ 1]: *
10.0000 - 20.0000 [ 0]:
20.0000 - 30.0000 [ 0]:
30.0000 - 40.0000 [ 11]: ***********
40.0000 - 50.0000 [ 49]:
*************************************************
50.0000 - 60.0000 [ 0]:
60.0000 - 70.0000 [ 0]:
70.0000 - 80.0000 [ 0]:
80.0000 - 90.0000 [ 0]:
90.0000 - 100.0000 [ 0]:-----------------------------------------------------------
3.10-rc2 perfteam2 RX (reverts commit
e11538d1f03914eb92af5a1a378375c05ae8520c)
TCP_RR trans/s 49698.69Receiver %c0
0.0000 - 10.0000 [ 1]: *
10.0000 - 20.0000 [ 1]: *
20.0000 - 30.0000 [ 0]:
30.0000 - 40.0000 [ 59]:
***********************************************************
40.0000 - 50.0000 [ 0]:
50.0000 - 60.0000 [ 0]:
60.0000 - 70.0000 [ 0]:
70.0000 - 80.0000 [ 0]:
80.0000 - 90.0000 [ 0]:
90.0000 - 100.0000 [ 0]:Sender %c0
0.0000 - 10.0000 [ 1]: *
10.0000 - 20.0000 [ 0]:
20.0000 - 30.0000 [ 0]:
30.0000 - 40.0000 [ 2]: **
40.0000 - 50.0000 [ 58]:
**********************************************************
50.0000 - 60.0000 [ 0]:
60.0000 - 70.0000 [ 0]:
70.0000 - 80.0000 [ 0]:
80.0000 - 90.0000 [ 0]:
90.0000 - 100.0000 [ 0]:-----------------------------------------------------------
3.10-rc2 test RX (reverts 69a37beabf1f0a6705c08e879bdd5d82ff6486c4
and e11538d1f03914eb92af5a1a378375c05ae8520c)
TCP_RR trans/s 47766.95Receiver %c0
0.0000 - 10.0000 [ 1]: *
10.0000 - 20.0000 [ 1]: *
20.0000 - 30.0000 [ 0]:
30.0000 - 40.0000 [ 27]: ***************************
40.0000 - 50.0000 [ 2]: **
50.0000 - 60.0000 [ 0]:
60.0000 - 70.0000 [ 2]: **
70.0000 - 80.0000 [ 0]:
80.0000 - 90.0000 [ 0]:
90.0000 - 100.0000 [ 28]: ****************************Sender:
0.0000 - 10.0000 [ 1]: *
10.0000 - 20.0000 [ 0]:
20.0000 - 30.0000 [ 0]:
30.0000 - 40.0000 [ 11]: ***********
40.0000 - 50.0000 [ 0]:
50.0000 - 60.0000 [ 1]: *
60.0000 - 70.0000 [ 0]:
70.0000 - 80.0000 [ 3]: ***
80.0000 - 90.0000 [ 7]: *******
90.0000 - 100.0000 [ 38]: **************************************These results demonstrate gaining back the tendency of the CPU to
stay in more responsive, performant C-states (and thus yield
measurably better performance), by reverting commit
69a37beabf1f0a6705c08e879bdd5d82ff6486c4.Requested-by: Jeremy Eder
Tested-by: Len Brown
Signed-off-by: Rafael J. Wysocki
Signed-off-by: Greg Kroah-Hartman
31 May, 2013
1 commit
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In tick_nohz_cpu_down_callback() if the cpu is the one handling
timekeeping, we must return something that stops the CPU_DOWN_PREPARE
notifiers and then start notify CPU_DOWN_FAILED on the already called
notifier call backs.However traditional errno values are not handled by the notifier unless
these are encapsulated using errno_to_notifier().Hence the current -EINVAL is misinterpreted and converted to junk after
notifier_to_errno(), leaving the notifier subsystem to random behaviour
such as eventually allowing the cpu to go down.Fix this by using the standard NOTIFY_BAD instead.
Signed-off-by: Li Zhong
Reviewed-by: Srivatsa S. Bhat
Acked-by: Steven Rostedt
Cc: Paul E. McKenney
Cc: Ingo Molnar
Cc: Thomas Gleixner
Cc: Peter Zijlstra
Cc: Borislav Petkov
Signed-off-by: Frederic Weisbecker
Signed-off-by: Ingo Molnar
16 May, 2013
1 commit
-
Pull timer fixes from Thomas Gleixner:
- Cure for not using zalloc in the first place, which leads to random
crashes with CPUMASK_OFF_STACK.- Revert a user space visible change which broke udev
- Add a missing cpu_online early return introduced by the new full
dyntick conversions- Plug a long standing race in the timer wheel cpu hotplug code.
Sigh...- Cleanup NOHZ per cpu data on cpu down to prevent stale data on cpu
up.* 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
time: Revert ALWAYS_USE_PERSISTENT_CLOCK compile time optimizaitons
timer: Don't reinitialize the cpu base lock during CPU_UP_PREPARE
tick: Don't invoke tick_nohz_stop_sched_tick() if the cpu is offline
tick: Cleanup NOHZ per cpu data on cpu down
tick: Use zalloc_cpumask_var for allocating offstack cpumasks
14 May, 2013
1 commit
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commit 5b39939a4 (nohz: Move ts->idle_calls incrementation into strict
idle logic) moved code out of tick_nohz_stop_sched_tick() and missed
to bail out when the cpu is offline. That's causing subsequent
failures as an offline CPU is supposed to die and not to fiddle with
nohz magic.Return false in can_stop_idle_tick() if the cpu is offline.
Reported-and-tested-by: Jiri Kosina
Reported-and-tested-by: Prarit Bhargava
Cc: Frederic Weisbecker
Cc: Borislav Petkov
Cc: Tony Luck
Cc: x86@kernel.org
Link: http://lkml.kernel.org/r/alpine.LFD.2.02.1305132138160.2863@ionos
Signed-off-by: Thomas Gleixner
12 May, 2013
1 commit
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Prarit reported a crash on CPU offline/online. The reason is that on
CPU down the NOHZ related per cpu data of the dead cpu is not cleaned
up. If at cpu online an interrupt happens before the per cpu tick
device is registered the irq_enter() check potentially sees stale data
and dereferences a NULL pointer.Cleanup the data after the cpu is dead.
Reported-by: Prarit Bhargava
Cc: stable@vger.kernel.org
Cc: Mike Galbraith
Link: http://lkml.kernel.org/r/alpine.LFD.2.02.1305031451561.2886@ionos
Signed-off-by: Thomas Gleixner
06 May, 2013
1 commit
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Pull 'full dynticks' support from Ingo Molnar:
"This tree from Frederic Weisbecker adds a new, (exciting! :-) core
kernel feature to the timer and scheduler subsystems: 'full dynticks',
or CONFIG_NO_HZ_FULL=y.This feature extends the nohz variable-size timer tick feature from
idle to busy CPUs (running at most one task) as well, potentially
reducing the number of timer interrupts significantly.This feature got motivated by real-time folks and the -rt tree, but
the general utility and motivation of full-dynticks runs wider than
that:- HPC workloads get faster: CPUs running a single task should be able
to utilize a maximum amount of CPU power. A periodic timer tick at
HZ=1000 can cause a constant overhead of up to 1.0%. This feature
removes that overhead - and speeds up the system by 0.5%-1.0% on
typical distro configs even on modern systems.- Real-time workload latency reduction: CPUs running critical tasks
should experience as little jitter as possible. The last remaining
source of kernel-related jitter was the periodic timer tick.- A single task executing on a CPU is a pretty common situation,
especially with an increasing number of cores/CPUs, so this feature
helps desktop and mobile workloads as well.The cost of the feature is mainly related to increased timer
reprogramming overhead when a CPU switches its tick period, and thus
slightly longer to-idle and from-idle latency.Configuration-wise a third mode of operation is added to the existing
two NOHZ kconfig modes:- CONFIG_HZ_PERIODIC: [formerly !CONFIG_NO_HZ], now explicitly named
as a config option. This is the traditional Linux periodic tick
design: there's a HZ tick going on all the time, regardless of
whether a CPU is idle or not.- CONFIG_NO_HZ_IDLE: [formerly CONFIG_NO_HZ=y], this turns off the
periodic tick when a CPU enters idle mode.- CONFIG_NO_HZ_FULL: this new mode, in addition to turning off the
tick when a CPU is idle, also slows the tick down to 1 Hz (one
timer interrupt per second) when only a single task is running on a
CPU.The .config behavior is compatible: existing !CONFIG_NO_HZ and
CONFIG_NO_HZ=y settings get translated to the new values, without the
user having to configure anything. CONFIG_NO_HZ_FULL is turned off by
default.This feature is based on a lot of infrastructure work that has been
steadily going upstream in the last 2-3 cycles: related RCU support
and non-periodic cputime support in particular is upstream already.This tree adds the final pieces and activates the feature. The pull
request is marked RFC because:- it's marked 64-bit only at the moment - the 32-bit support patch is
small but did not get ready in time.- it has a number of fresh commits that came in after the merge
window. The overwhelming majority of commits are from before the
merge window, but still some aspects of the tree are fresh and so I
marked it RFC.- it's a pretty wide-reaching feature with lots of effects - and
while the components have been in testing for some time, the full
combination is still not very widely used. That it's default-off
should reduce its regression abilities and obviously there are no
known regressions with CONFIG_NO_HZ_FULL=y enabled either.- the feature is not completely idempotent: there is no 100%
equivalent replacement for a periodic scheduler/timer tick. In
particular there's ongoing work to map out and reduce its effects
on scheduler load-balancing and statistics. This should not impact
correctness though, there are no known regressions related to this
feature at this point.- it's a pretty ambitious feature that with time will likely be
enabled by most Linux distros, and we'd like you to make input on
its design/implementation, if you dislike some aspect we missed.
Without flaming us to crisp! :-)Future plans:
- there's ongoing work to reduce 1Hz to 0Hz, to essentially shut off
the periodic tick altogether when there's a single busy task on a
CPU. We'd first like 1 Hz to be exposed more widely before we go
for the 0 Hz target though.- once we reach 0 Hz we can remove the periodic tick assumption from
nr_running>=2 as well, by essentially interrupting busy tasks only
as frequently as the sched_latency constraints require us to do -
once every 4-40 msecs, depending on nr_running.I am personally leaning towards biting the bullet and doing this in
v3.10, like the -rt tree this effort has been going on for too long -
but the final word is up to you as usual.More technical details can be found in Documentation/timers/NO_HZ.txt"
* 'timers-nohz-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (39 commits)
sched: Keep at least 1 tick per second for active dynticks tasks
rcu: Fix full dynticks' dependency on wide RCU nocb mode
nohz: Protect smp_processor_id() in tick_nohz_task_switch()
nohz_full: Add documentation.
cputime_nsecs: use math64.h for nsec resolution conversion helpers
nohz: Select VIRT_CPU_ACCOUNTING_GEN from full dynticks config
nohz: Reduce overhead under high-freq idling patterns
nohz: Remove full dynticks' superfluous dependency on RCU tree
nohz: Fix unavailable tick_stop tracepoint in dynticks idle
nohz: Add basic tracing
nohz: Select wide RCU nocb for full dynticks
nohz: Disable the tick when irq resume in full dynticks CPU
nohz: Re-evaluate the tick for the new task after a context switch
nohz: Prepare to stop the tick on irq exit
nohz: Implement full dynticks kick
nohz: Re-evaluate the tick from the scheduler IPI
sched: New helper to prevent from stopping the tick in full dynticks
sched: Kick full dynticks CPU that have more than one task enqueued.
perf: New helper to prevent full dynticks CPUs from stopping tick
perf: Kick full dynticks CPU if events rotation is needed
...
04 May, 2013
1 commit
-
The scheduler doesn't yet fully support environments
with a single task running without a periodic tick.In order to ensure we still maintain the duties of scheduler_tick(),
keep at least 1 tick per second.This makes sure that we keep the progression of various scheduler
accounting and background maintainance even with a very low granularity.
Examples include cpu load, sched average, CFS entity vruntime,
avenrun and events such as load balancing, amongst other details
handled in sched_class::task_tick().This limitation will be removed in the future once we get
these individual items to work in full dynticks CPUs.Suggested-by: Ingo Molnar
Signed-off-by: Frederic Weisbecker
Cc: Christoph Lameter
Cc: Hakan Akkan
Cc: Ingo Molnar
Cc: Kevin Hilman
Cc: Li Zhong
Cc: Paul E. McKenney
Cc: Paul Gortmaker
Cc: Peter Zijlstra
Cc: Steven Rostedt
Cc: Thomas Gleixner
29 Apr, 2013
1 commit
-
I saw following error when testing the latest nohz code on
Power:[ 85.295384] BUG: using smp_processor_id() in preemptible [00000000] code: rsyslogd/3493
[ 85.295396] caller is .tick_nohz_task_switch+0x1c/0xb8
[ 85.295402] Call Trace:
[ 85.295408] [c0000001fababab0] [c000000000012dc4] .show_stack+0x110/0x25c (unreliable)
[ 85.295420] [c0000001fababba0] [c0000000007c4b54] .dump_stack+0x20/0x30
[ 85.295430] [c0000001fababc10] [c00000000044eb74] .debug_smp_processor_id+0xf4/0x124
[ 85.295438] [c0000001fababca0] [c0000000000d7594] .tick_nohz_task_switch+0x1c/0xb8
[ 85.295447] [c0000001fababd20] [c0000000000b9748] .finish_task_switch+0x13c/0x160
[ 85.295455] [c0000001fababdb0] [c0000000000bbe50] .schedule_tail+0x50/0x124
[ 85.295463] [c0000001fababe30] [c000000000009dc8] .ret_from_fork+0x4/0x54The code below moves the test into local_irq_save/restore
section to avoid the above complaint.Signed-off-by: Li Zhong
Acked-by: Frederic Weisbecker
Cc: Peter Zijlstra
Cc: Paul McKenney
Link: http://lkml.kernel.org/r/1367119558.6391.34.camel@ThinkPad-T5421.cn.ibm.com
Signed-off-by: Ingo Molnar
26 Apr, 2013
1 commit
-
One testbox of mine (Intel Nehalem, 16-way) uses MWAIT for its idle routine,
which apparently can break out of its idle loop rather frequently, with
high frequency.In that case NO_HZ_FULL=y kernels show high ksoftirqd overhead and constant
context switching, because tick_nohz_stop_sched_tick() will, if
delta_jiffies == 0, mis-identify this as a timer event - activating the
TIMER_SOFTIRQ, which wakes up ksoftirqd.Fix this by treating delta_jiffies == 0 the same way we treat other short
wakeups, delta_jiffies == 1.Cc: Frederic Weisbecker
Cc: Chris Metcalf
Cc: Christoph Lameter
Cc: Geoff Levand
Cc: Gilad Ben Yossef
Cc: Hakan Akkan
Cc: Kevin Hilman
Cc: Li Zhong
Cc: Oleg Nesterov
Cc: Paul E. McKenney
Cc: Paul Gortmaker
Cc: Peter Zijlstra
Cc: Steven Rostedt
Signed-off-by: Ingo Molnar
23 Apr, 2013
5 commits
-
It's not obvious to find out why the full dynticks subsystem
doesn't always stop the tick: whether this is due to kthreads,
posix timers, perf events, etc...These new tracepoints are here to help the user diagnose
the failures and test this feature.Signed-off-by: Frederic Weisbecker
Cc: Chris Metcalf
Cc: Christoph Lameter
Cc: Geoff Levand
Cc: Gilad Ben Yossef
Cc: Hakan Akkan
Cc: Ingo Molnar
Cc: Kevin Hilman
Cc: Li Zhong
Cc: Oleg Nesterov
Cc: Paul E. McKenney
Cc: Paul Gortmaker
Cc: Peter Zijlstra
Cc: Steven Rostedt
Cc: Thomas Gleixner -
When a task is scheduled in, it may have some properties
of its own that could make the CPU reconsider the need for
the tick: posix cpu timers, perf events, ...So notify the full dynticks subsystem when a task gets
scheduled in and re-check the tick dependency at this
stage. This is done through a self IPI to avoid messing
up with any current lock scenario.Signed-off-by: Frederic Weisbecker
Cc: Chris Metcalf
Cc: Christoph Lameter
Cc: Geoff Levand
Cc: Gilad Ben Yossef
Cc: Hakan Akkan
Cc: Ingo Molnar
Cc: Kevin Hilman
Cc: Li Zhong
Cc: Oleg Nesterov
Cc: Paul E. McKenney
Cc: Paul Gortmaker
Cc: Peter Zijlstra
Cc: Steven Rostedt
Cc: Thomas Gleixner -
Interrupt exit is a natural place to stop the tick: it happens
after all events happening before and during the irq which
are liable to update the dependency on the tick occured. Also
it makes sure that any check on tick dependency is well ordered
against dynticks kick IPIs.Bring in the infrastructure that performs the tick dependency
checks on irq exit and shut it down if these checks show that we
can do it safely.Signed-off-by: Frederic Weisbecker
Cc: Chris Metcalf
Cc: Christoph Lameter
Cc: Geoff Levand
Cc: Gilad Ben Yossef
Cc: Hakan Akkan
Cc: Ingo Molnar
Cc: Kevin Hilman
Cc: Li Zhong
Cc: Oleg Nesterov
Cc: Paul E. McKenney
Cc: Paul Gortmaker
Cc: Peter Zijlstra
Cc: Steven Rostedt
Cc: Thomas Gleixner -
Implement the full dynticks kick that is performed from
IPIs sent by various subsystems (scheduler, posix timers, ...)
when they want to notify about a new event that may
reconsider the dependency on the tick.Most of the time, such an event end up restarting the tick.
(Part of the design with subsystems providing *_can_stop_tick()
helpers suggested by Peter Zijlstra a while ago).Signed-off-by: Frederic Weisbecker
Cc: Chris Metcalf
Cc: Christoph Lameter
Cc: Geoff Levand
Cc: Gilad Ben Yossef
Cc: Hakan Akkan
Cc: Ingo Molnar
Cc: Kevin Hilman
Cc: Li Zhong
Cc: Oleg Nesterov
Cc: Paul E. McKenney
Cc: Paul Gortmaker
Cc: Peter Zijlstra
Cc: Steven Rostedt
Cc: Thomas Gleixner -
The scheduler IPI is used by the scheduler to kick
full dynticks CPUs asynchronously when more than one
task are running or when a new timer list timer is
enqueued. This way the destination CPU can decide
to restart the tick to handle this new situation.Now let's call that kick in the scheduler IPI.
(Reusing the scheduler IPI rather than implementing
a new IPI was suggested by Peter Zijlstra a while ago)Signed-off-by: Frederic Weisbecker
Cc: Chris Metcalf
Cc: Christoph Lameter
Cc: Geoff Levand
Cc: Gilad Ben Yossef
Cc: Hakan Akkan
Cc: Ingo Molnar
Cc: Kevin Hilman
Cc: Li Zhong
Cc: Oleg Nesterov
Cc: Paul E. McKenney
Cc: Paul Gortmaker
Cc: Peter Zijlstra
Cc: Steven Rostedt
Cc: Thomas Gleixner
21 Apr, 2013
1 commit
-
…/kernel/git/frederic/linux-dynticks into timers/nohz
Pull posix cpu timers handling on full dynticks from Frederic Weisbecker.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
19 Apr, 2013
4 commits
-
Provide a new kernel config that defaults all CPUs to be part
of the full dynticks range, except the boot one for timekeeping.This default setting is overriden by the nohz_full= boot option
if passed by the user.This is helpful for those who don't need a finegrained range
of full dynticks CPU and also for automated testing.Suggested-by: Ingo Molnar
Reviewed-by: Paul E. McKenney
Signed-off-by: Frederic Weisbecker
Cc: Andrew Morton
Cc: Chris Metcalf
Cc: Christoph Lameter
Cc: Geoff Levand
Cc: Gilad Ben Yossef
Cc: Hakan Akkan
Cc: Ingo Molnar
Cc: Kevin Hilman
Cc: Li Zhong
Cc: Paul E. McKenney
Cc: Paul Gortmaker
Cc: Peter Zijlstra
Cc: Steven Rostedt
Cc: Thomas Gleixner -
We need full dynticks CPU to also be RCU nocb so
that we don't have to keep the tick to handle RCU
callbacks.Make sure the range passed to nohz_full= boot
parameter is a subset of rcu_nocbs=The CPUs that fail to meet this requirement will be
excluded from the nohz_full range. This is checked
early in boot time, before any CPU has the opportunity
to stop its tick.Suggested-by: Steven Rostedt
Reviewed-by: Paul E. McKenney
Signed-off-by: Frederic Weisbecker
Cc: Andrew Morton
Cc: Chris Metcalf
Cc: Christoph Lameter
Cc: Geoff Levand
Cc: Gilad Ben Yossef
Cc: Hakan Akkan
Cc: Ingo Molnar
Cc: Kevin Hilman
Cc: Li Zhong
Cc: Paul E. McKenney
Cc: Paul Gortmaker
Cc: Peter Zijlstra
Cc: Steven Rostedt
Cc: Thomas Gleixner -
The timekeeping job must be able to run early on boot
because there may be some pre-SMP (and thus pre-initcalls )
components that rely on it. The IO-APIC is one such users
as it tests the timer health by watching jiffies progression.Given that it happens before we know the initial online
set, we can't rely on it to select a timekeeper. We need
one before SMP time otherwise we simply crash on boot.To fix this and keep things simple for now, force the boot CPU
outside of the full dynticks range in any case and do this early
on kernel parameter parsing time.We might want a trickier solution later, expecially for aSMP
architectures that need to assign housekeeping tasks to arbitrary
low power CPUs.But it's still first pass KISS time for now.
Reviewed-by: Paul E. McKenney
Signed-off-by: Frederic Weisbecker
Cc: Andrew Morton
Cc: Chris Metcalf
Cc: Christoph Lameter
Cc: Geoff Levand
Cc: Gilad Ben Yossef
Cc: Hakan Akkan
Cc: Ingo Molnar
Cc: Kevin Hilman
Cc: Li Zhong
Cc: Paul E. McKenney
Cc: Paul Gortmaker
Cc: Peter Zijlstra
Cc: Steven Rostedt
Cc: Thomas Gleixner -
Provide two new helpers in order to notify the full dynticks CPUs about
some internal system changes against which they may reconsider the state
of their tick. Some practical examples include: posix cpu timers, perf tick
and sched clock tick.For now the notifying handler, implemented through IPIs, is a stub
that will be implemented when we get the tick stop/restart infrastructure
in.Signed-off-by: Frederic Weisbecker
Cc: Chris Metcalf
Cc: Christoph Lameter
Cc: Geoff Levand
Cc: Gilad Ben Yossef
Cc: Hakan Akkan
Cc: Ingo Molnar
Cc: Kevin Hilman
Cc: Li Zhong
Cc: Oleg Nesterov
Cc: Paul E. McKenney
Cc: Paul Gortmaker
Cc: Peter Zijlstra
Cc: Steven Rostedt
Cc: Thomas Gleixner
16 Apr, 2013
1 commit
-
"Extended nohz" was used as a naming base for the full dynticks
API and Kconfig symbols. It reflects the fact the system tries
to stop the tick in more places than just idle.But that "extended" name is a bit opaque and vague. Rename it to
"full" makes it clearer what the system tries to do under this
config: try to shutdown the tick anytime it can. The various
constraints that prevent that to happen shouldn't be considered
as fundamental properties of this feature but rather technical
issues that may be solved in the future.Reported-by: Ingo Molnar
Signed-off-by: Frederic Weisbecker
Cc: Chris Metcalf
Cc: Christoph Lameter
Cc: Geoff Levand
Cc: Gilad Ben Yossef
Cc: Hakan Akkan
Cc: Ingo Molnar
Cc: Kevin Hilman
Cc: Li Zhong
Cc: Paul E. McKenney
Cc: Paul Gortmaker
Cc: Peter Zijlstra
Cc: Steven Rostedt
Cc: Thomas Gleixner
03 Apr, 2013
2 commits
-
Given that we apply a few restrictions on the full dynticks
CPUs range (keep an online timekeeper oustide the range,
then in the future have the range be an RCU nocb CPUs subset),
let's print the final resulting range of full dynticks CPUs to
the user so that he knows what's really going to run.Signed-off-by: Frederic Weisbecker
Cc: Andrew Morton
Cc: Chris Metcalf
Cc: Christoph Lameter
Cc: Geoff Levand
Cc: Gilad Ben Yossef
Cc: Hakan Akkan
Cc: Ingo Molnar
Cc: Kevin Hilman
Cc: Li Zhong
Cc: Namhyung Kim
Cc: Paul E. McKenney
Cc: Paul Gortmaker
Cc: Peter Zijlstra
Cc: Steven Rostedt
Cc: Thomas Gleixner -
We are planning to convert the dynticks Kconfig options layout
into a choice menu. The user must be able to easily pick
any of the following implementations: constant periodic tick,
idle dynticks, full dynticks.As this implies a mutual exclusion, the two dynticks implementions
need to converge on the selection of a common Kconfig option in order
to ease the sharing of a common infrastructure.It would thus seem pretty natural to reuse CONFIG_NO_HZ to
that end. It already implements all the idle dynticks code
and the full dynticks depends on all that code for now.
So ideally the choice menu would propose CONFIG_NO_HZ_IDLE and
CONFIG_NO_HZ_EXTENDED then both would select CONFIG_NO_HZ.On the other hand we want to stay backward compatible: if
CONFIG_NO_HZ is set in an older config file, we want to
enable CONFIG_NO_HZ_IDLE by default.But we can't afford both at the same time or we run into
a circular dependency:1) CONFIG_NO_HZ_IDLE and CONFIG_NO_HZ_EXTENDED both select
CONFIG_NO_HZ
2) If CONFIG_NO_HZ is set, we default to CONFIG_NO_HZ_IDLEWe might be able to support that from Kconfig/Kbuild but it
may not be wise to introduce such a confusing behaviour.So to solve this, create a new CONFIG_NO_HZ_COMMON option
which gathers the common code between idle and full dynticks
(that common code for now is simply the idle dynticks code)
and select it from their referring Kconfig.Then we'll later create CONFIG_NO_HZ_IDLE and map CONFIG_NO_HZ
to it for backward compatibility.Signed-off-by: Frederic Weisbecker
Cc: Andrew Morton
Cc: Chris Metcalf
Cc: Christoph Lameter
Cc: Geoff Levand
Cc: Gilad Ben Yossef
Cc: Hakan Akkan
Cc: Ingo Molnar
Cc: Kevin Hilman
Cc: Li Zhong
Cc: Namhyung Kim
Cc: Paul E. McKenney
Cc: Paul Gortmaker
Cc: Peter Zijlstra
Cc: Steven Rostedt
Cc: Thomas Gleixner
25 Mar, 2013
1 commit
-
The "NOHZ: local_softirq_pending" message is a largely informational
message. This makes extra work for customers that have a policy of
investigating all kernel log messages logged at
Cc: Don Zickus
Link: http://lkml.kernel.org/r/2037057938.893524.1360345050772.JavaMail.root@redhat.com
Signed-off-by: Thomas Gleixner
21 Mar, 2013
2 commits
-
This way the full nohz CPUs can safely run with the tick
stopped with a guarantee that somebody else is taking
care of the jiffies and GTOD progression.Once the duty is attributed to a CPU, it won't change. Also that
CPU can't enter into dyntick idle mode or be hot unplugged.This may later be improved from a power consumption POV. At
least we should be able to share the duty amongst all CPUs
outside the full dynticks range. Then the duty could even be
shared with full dynticks CPUs when those can't stop their
tick for any reason.But let's start with that very simple approach first.
Signed-off-by: Frederic Weisbecker
Cc: Andrew Morton
Cc: Chris Metcalf
Cc: Christoph Lameter
Cc: Geoff Levand
Cc: Gilad Ben Yossef
Cc: Hakan Akkan
Cc: Ingo Molnar
Cc: Kevin Hilman
Cc: Li Zhong
Cc: Namhyung Kim
Cc: Paul E. McKenney
Cc: Paul Gortmaker
Cc: Peter Zijlstra
Cc: Steven Rostedt
Cc: Thomas Gleixner
[fix have_nohz_full_mask offcase]
Signed-off-by: Steven Rostedt -
For extreme usecases such as Real Time or HPC, having
the ability to shutdown the tick when a single task runs
on a CPU is a desired feature:* Reducing the amount of interrupts improves throughput
for CPU-bound tasks. The CPU is less distracted from its
real job, from an execution time and from the cache point
of views.* This also improve latency response as we have less critical
sections.Start with introducing a very simple interface to define
full dynticks CPU: use a boot time option defined cpumask
through the "nohz_extended=" kernel parameter. CPUs that
are part of this range will have their tick shutdown
whenever possible: provided they run a single task and
they don't do kernel activity that require the periodic
tick. These details will be later documented in
Documentation/*An online CPU must be kept outside this range to handle the
timekeeping.Suggested-by: Paul E. McKenney
Signed-off-by: Frederic Weisbecker
Cc: Andrew Morton
Cc: Chris Metcalf
Cc: Christoph Lameter
Cc: Geoff Levand
Cc: Gilad Ben Yossef
Cc: Hakan Akkan
Cc: Ingo Molnar
Cc: Kevin Hilman
Cc: Li Zhong
Cc: Namhyung Kim
Cc: Paul E. McKenney
Cc: Paul Gortmaker
Cc: Peter Zijlstra
Cc: Steven Rostedt
Cc: Thomas Gleixner
01 Mar, 2013
1 commit
-
Pull thermal management updates from Zhang Rui:
"Highlights:- introduction of Dove thermal sensor driver.
- introduction of Kirkwood thermal sensor driver.
- introduction of intel_powerclamp thermal cooling device driver.
- add interrupt and DT support for rcar thermal driver.
- add thermal emulation support which allows platform thermal driver
to do software/hardware emulation for thermal issues."* 'release' of git://git.kernel.org/pub/scm/linux/kernel/git/rzhang/linux: (36 commits)
thermal: rcar: remove __devinitconst
thermal: return an error on failure to register thermal class
Thermal: rename thermal governor Kconfig option to avoid generic naming
thermal: exynos: Use the new thermal trend type for quick cooling action.
Thermal: exynos: Add support for temperature falling interrupt.
Thermal: Dove: Add Themal sensor support for Dove.
thermal: Add support for the thermal sensor on Kirkwood SoCs
thermal: rcar: add Device Tree support
thermal: rcar: remove machine_power_off() from rcar_thermal_notify()
thermal: rcar: add interrupt support
thermal: rcar: add read/write functions for common/priv data
thermal: rcar: multi channel support
thermal: rcar: use mutex lock instead of spin lock
thermal: rcar: enable CPCTL to use hardware TSC deciding
thermal: rcar: use parenthesis on macro
Thermal: fix a build warning when CONFIG_THERMAL_EMULATION cleared
Thermal: fix a wrong comment
thermal: sysfs: Add a new sysfs node emul_temp for thermal emulation
PM: intel_powerclamp: off by one in start_power_clamp()
thermal: exynos: Miscellaneous fixes to support falling threshold interrupt
...
20 Feb, 2013
1 commit
-
Pull scheduler changes from Ingo Molnar:
"Main changes:- scheduler side full-dynticks (user-space execution is undisturbed
and receives no timer IRQs) preparation changes that convert the
cputime accounting code to be full-dynticks ready, from Frederic
Weisbecker.- Initial sched.h split-up changes, by Clark Williams
- select_idle_sibling() performance improvement by Mike Galbraith:
" 1 tbench pair (worst case) in a 10 core + SMT package:
pre 15.22 MB/sec 1 procs
post 252.01 MB/sec 1 procs "- sched_rr_get_interval() ABI fix/change. We think this detail is not
used by apps (so it's not an ABI in practice), but lets keep it
under observation.- misc RT scheduling cleanups, optimizations"
* 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (24 commits)
sched/rt: Add header to
cputime: Remove irqsave from seqlock readers
sched, powerpc: Fix sched.h split-up build failure
cputime: Restore CPU_ACCOUNTING config defaults for PPC64
sched/rt: Move rt specific bits into new header file
sched/rt: Add a tuning knob to allow changing SCHED_RR timeslice
sched: Move sched.h sysctl bits into separate header
sched: Fix signedness bug in yield_to()
sched: Fix select_idle_sibling() bouncing cow syndrome
sched/rt: Further simplify pick_rt_task()
sched/rt: Do not account zero delta_exec in update_curr_rt()
cputime: Safely read cputime of full dynticks CPUs
kvm: Prepare to add generic guest entry/exit callbacks
cputime: Use accessors to read task cputime stats
cputime: Allow dynamic switch between tick/virtual based cputime accounting
cputime: Generic on-demand virtual cputime accounting
cputime: Move default nsecs_to_cputime() to jiffies based cputime file
cputime: Librarize per nsecs resolution cputime definitions
cputime: Avoid multiplication overflow on utime scaling
context_tracking: Export context state for generic vtime
...Fix up conflict in kernel/context_tracking.c due to comment additions.
05 Feb, 2013
1 commit
-
Conflicts:
kernel/irq_work.cAdd support for printk in full dynticks CPU.
* Don't stop tick with irq works pending. This
fix is generally useful and concerns archs that
can't raise self IPIs.* Flush irq works before CPU offlining.
* Introduce "lazy" irq works that can wait for the
next tick to be executed, unless it's stopped.* Implement klogd wake up using irq work. This
removes the ad-hoc printk_tick()/printk_needs_cpu()
hooks and make it working even in dynticks mode.Signed-off-by: Frederic Weisbecker
28 Jan, 2013
1 commit
-
Allow to dynamically switch between tick and virtual based
cputime accounting. This way we can provide a kind of "on-demand"
virtual based cputime accounting. In this mode, the kernel relies
on the context tracking subsystem to dynamically probe on kernel
boundaries.This is in preparation for being able to stop the timer tick in
more places than just the idle state. Doing so will depend on
CONFIG_VIRT_CPU_ACCOUNTING_GEN which makes it possible to account
the cputime without the tick by hooking on kernel/user boundaries.Depending whether the tick is stopped or not, we can switch between
tick and vtime based accounting anytime in order to minimize the
overhead associated to user hooks.Signed-off-by: Frederic Weisbecker
Cc: Andrew Morton
Cc: Ingo Molnar
Cc: Li Zhong
Cc: Namhyung Kim
Cc: Paul E. McKenney
Cc: Paul Gortmaker
Cc: Peter Zijlstra
Cc: Steven Rostedt
Cc: Thomas Gleixner
17 Jan, 2013
1 commit
-
Allow drivers such as intel_powerclamp to use these apis for
turning on/off ticks during idle.Signed-off-by: Jacob Pan
Signed-off-by: Zhang Rui
12 Dec, 2012
2 commits
-
Pull core timer changes from Ingo Molnar:
"It contains continued generic-NOHZ work by Frederic and smaller
cleanups."* 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
time: Kill xtime_lock, replacing it with jiffies_lock
clocksource: arm_generic: use this_cpu_ptr per-cpu helper
clocksource: arm_generic: use integer math helpers
time/jiffies: Make clocksource_jiffies static
clocksource: clean up parse_pmtmr()
tick: Correct the comments for tick_sched_timer()
tick: Conditionally build nohz specific code in tick handler
tick: Consolidate tick handling for high and low res handlers
tick: Consolidate timekeeping handling code -
…it.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull trivial fix branches from Ingo Molnar.
Cleanup in __get_key_name, and a timer comment fixlet.
* 'core-locking-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
lockdep: Use KSYM_NAME_LEN'ed buffer for __get_key_name()* 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
timers, sched: Correct the comments for tick_sched_timer()
22 Nov, 2012
1 commit
-
Fix trivial conflicts in: kernel/time/tick-sched.c
Signed-off-by: Thomas Gleixner
18 Nov, 2012
3 commits
-
klogd is woken up asynchronously from the tick in order
to do it safely.However if printk is called when the tick is stopped, the reader
won't be woken up until the next interrupt, which might not fire
for a while. As a result, the user may miss some message.To fix this, lets implement the printk tick using a lazy irq work.
This subsystem takes care of the timer tick state and can
fix up accordingly.Signed-off-by: Frederic Weisbecker
Acked-by: Steven Rostedt
Cc: Peter Zijlstra
Cc: Thomas Gleixner
Cc: Ingo Molnar
Cc: Andrew Morton
Cc: Paul Gortmaker -
Don't stop the tick if we have pending irq works on the
queue, otherwise if the arch can't raise self-IPIs, we may not
find an opportunity to execute the pending works for a while.Signed-off-by: Frederic Weisbecker
Acked-by: Steven Rostedt
Cc: Peter Zijlstra
Cc: Thomas Gleixner
Cc: Ingo Molnar
Cc: Andrew Morton
Cc: Paul Gortmaker -
We need some quick way to check if the CPU has stopped
its tick. This will be useful to implement the printk tick
using the irq work subsystem.Signed-off-by: Frederic Weisbecker
Acked-by: Steven Rostedt
Cc: Peter Zijlstra
Cc: Thomas Gleixner
Cc: Ingo Molnar
Cc: Andrew Morton
Cc: Paul Gortmaker
15 Nov, 2012
1 commit
-
The prediction for future is difficult and when the cpuidle governor prediction
fails and govenor possibly choose the shallower C-state than it should. How to
quickly notice and find the failure becomes important for power saving.cpuidle menu governor has a method to predict the repeat pattern if there are 8
C-states residency which are continuous and the same or very close, so it will
predict the next C-states residency will keep same residency time.There is a real case that turbostat utility (tools/power/x86/turbostat)
at kernel 3.3 or early. turbostat utility will read 10 registers one by one at
Sandybridge, so it will generate 10 IPIs to wake up idle CPUs. So cpuidle menu
governor will predict it is repeat mode and there is another IPI wake up idle
CPU soon, so it keeps idle CPU stay at C1 state even though CPU is totally
idle. However, in the turbostat, following 10 registers reading is sleep 5
seconds by default, so the idle CPU will keep at C1 for a long time though it is
idle until break event occurs.
In a idle Sandybridge system, run "./turbostat -v", we will notice that deep
C-state dangles between "70% ~ 99%". After patched the kernel, we will notice
deep C-state stays at >99.98%.In the patch, a timer is added when menu governor detects a repeat mode and
choose a shallow C-state. The timer is set to a time out value that greater
than predicted time, and we conclude repeat mode prediction failure if timer is
triggered. When repeat mode happens as expected, the timer is not triggered
and CPU waken up from C-states and it will cancel the timer initiatively.
When repeat mode does not happen, the timer will be time out and menu governor
will quickly notice that the repeat mode prediction fails and then re-evaluates
deeper C-states possibility.Below is another case which will clearly show the patch much benefit:
#include
#include
#include
#include
#include
#include
#includevolatile int * shutdown;
volatile long * count;
int delay = 20;
int loop = 8;void usage(void)
{
fprintf(stderr,
"Usage: idle_predict [options]\n"
" --help -h Print this help\n"
" --thread -n Thread number\n"
" --loop -l Loop times in shallow Cstate\n"
" --delay -t Sleep time (uS)in shallow Cstate\n");
}void *simple_loop() {
int idle_num = 1;
while (!(*shutdown)) {
*count = *count + 1;if (idle_num % loop)
usleep(delay);
else {
/* sleep 1 second */
usleep(1000000);
idle_num = 0;
}
idle_num++;
}}
static void sighand(int sig)
{
*shutdown = 1;
}int main(int argc, char *argv[])
{
sigset_t sigset;
int signum = SIGALRM;
int i, c, er = 0, thread_num = 8;
pthread_t pt[1024];static char optstr[] = "n:l:t:h:";
while ((c = getopt(argc, argv, optstr)) != EOF)
switch (c) {
case 'n':
thread_num = atoi(optarg);
break;
case 'l':
loop = atoi(optarg);
break;
case 't':
delay = atoi(optarg);
break;
case 'h':
default:
usage();
exit(1);
}printf("thread=%d,loop=%d,delay=%d\n",thread_num,loop,delay);
count = malloc(sizeof(long));
shutdown = malloc(sizeof(int));
*count = 0;
*shutdown = 0;sigemptyset(&sigset);
sigaddset(&sigset, signum);
sigprocmask (SIG_BLOCK, &sigset, NULL);
signal(SIGINT, sighand);
signal(SIGTERM, sighand);for(i = 0; i < thread_num ; i++)
pthread_create(&pt[i], NULL, simple_loop, NULL);for (i = 0; i < thread_num; i++)
pthread_join(pt[i], NULL);exit(0);
}Get powertop V2 from git://github.com/fenrus75/powertop, build powertop.
After build the above test application, then run it.
Test plaform can be Intel Sandybridge or other recent platforms.
#./idle_predict -l 10 &
#./powertopWe will find that deep C-state will dangle between 40%~100% and much time spent
on C1 state. It is because menu governor wrongly predict that repeat mode
is kept, so it will choose the C1 shallow C-state even though it has chance to
sleep 1 second in deep C-state.While after patched the kernel, we find that deep C-state will keep >99.6%.
Signed-off-by: Rik van Riel
Signed-off-by: Youquan Song
Signed-off-by: Rafael J. Wysocki
14 Nov, 2012
1 commit
-
Now that timekeeping is protected by its own locks, rename
the xtime_lock to jifffies_lock to better describe what it
protects.CC: Thomas Gleixner
CC: Eric Dumazet
CC: Richard Cochran
Signed-off-by: John Stultz
01 Nov, 2012
1 commit
-
In the comments of function tick_sched_timer(), the sentence
"timer->base->cpu_base->lock held" is not right.In function __run_hrtimer(), before call timer->function(),
the cpu_base->lock has been unlocked.Signed-off-by: liu chuansheng
Cc: fei.li@intel.com
Cc: Peter Zijlstra
Link: http://lkml.kernel.org/r/1351098455.15558.1421.camel@cliu38-desktop-build
Signed-off-by: Thomas Gleixner
24 Oct, 2012
1 commit
-
In the comments of function tick_sched_timer(), the sentence
"timer->base->cpu_base->lock held" is not right.In function __run_hrtimer(), before call timer->function(),
the cpu_base->lock has been unlocked.Signed-off-by: liu chuansheng
Cc: fei.li@intel.com
Cc: Peter Zijlstra
Link: http://lkml.kernel.org/r/1351098455.15558.1421.camel@cliu38-desktop-build
Signed-off-by: Ingo Molnar