24 Nov, 2015
1 commit
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This is much less error-prone than the old code.
Signed-off-by: Andy Lutomirski
Cc: Andy Lutomirski
Cc: Borislav Petkov
Cc: Brian Gerst
Cc: Denys Vlasenko
Cc: Frederic Weisbecker
Cc: H. Peter Anvin
Cc: Linus Torvalds
Cc: Peter Zijlstra
Cc: Thomas Gleixner
Link: http://lkml.kernel.org/r/812df7e64f120c5c7c08481f36a8caa9f53b2199.1447361906.git.luto@kernel.org
Signed-off-by: Ingo Molnar
10 Nov, 2015
2 commits
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guest_enter and guest_exit must be called with interrupts disabled,
since they take the vtime_seqlock with write_seq{lock,unlock}.
Therefore, it is not necessary to check for exceptions, nor to
save/restore the IRQ state, when context tracking functions are
called by guest_enter and guest_exit.Split the body of context_tracking_entry and context_tracking_exit
out to __-prefixed functions, and use them from KVM.Rik van Riel has measured this to speed up a tight vmentry/vmexit
loop by about 2%.Cc: Andy Lutomirski
Cc: Frederic Weisbecker
Cc: Paul McKenney
Reviewed-by: Rik van Riel
Tested-by: Rik van Riel
Signed-off-by: Paolo Bonzini -
All calls to context_tracking_enter and context_tracking_exit
are already checking context_tracking_is_enabled, except the
context_tracking_user_enter and context_tracking_user_exit
functions left in for the benefit of assembly calls.Pull the check up to those functions, by making them simple
wrappers around the user_enter and user_exit inline functions.Cc: Frederic Weisbecker
Cc: Paul McKenney
Reviewed-by: Rik van Riel
Tested-by: Rik van Riel
Acked-by: Andy Lutomirski
Signed-off-by: Paolo Bonzini
07 May, 2015
2 commits
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TIF_NOHZ is used by context_tracking to force syscall slow-path
on every task in order to track userspace roundtrips. As such,
it must be set on all running tasks.It's currently explicitly inherited through context switches.
There is no need to do it in this fast-path though. The flag
could simply be set once for all on all tasks, whether they are
running or not.Lets do this by setting the flag for the init task on early boot,
and let it propagate through fork inheritance.While at it, mark context_tracking_cpu_set() as init code, we
only need it at early boot time.Suggested-by: Oleg Nesterov
Signed-off-by: Frederic Weisbecker
Reviewed-by: Rik van Riel
Cc: Borislav Petkov
Cc: Chris Metcalf
Cc: Dave Jones
Cc: H. Peter Anvin
Cc: Martin Schwidefsky
Cc: Mike Galbraith
Cc: Paul E . McKenney
Cc: Paul E. McKenney
Cc: Peter Zijlstra
Cc: Rafael J . Wysocki
Cc: Thomas Gleixner
Link: http://lkml.kernel.org/r/1430928266-24888-3-git-send-email-fweisbec@gmail.com
Signed-off-by: Ingo Molnar -
Context tracking recursion can happen when an exception triggers
in the middle of a call to a context tracking probe.This special case can be caused by vmalloc faults. If an access
to a memory area allocated by vmalloc happens in the middle of
context_tracking_enter(), we may run into an endless fault loop
because the exception in turn calls context_tracking_enter()
which faults on the same vmalloc'ed memory, triggering an
exception again, etc...Some rare crashes have been reported so lets protect against
this with a recursion counter.Reported-by: Dave Jones
Signed-off-by: Frederic Weisbecker
Reviewed-by: Rik van Riel
Acked-by: Peter Zijlstra (Intel)
Cc: Borislav Petkov
Cc: Chris Metcalf
Cc: H. Peter Anvin
Cc: Martin Schwidefsky
Cc: Mike Galbraith
Cc: Oleg Nesterov
Cc: Paul E. McKenney
Cc: Rafael J . Wysocki
Cc: Thomas Gleixner
Link: http://lkml.kernel.org/r/1430928266-24888-2-git-send-email-fweisbec@gmail.com
Signed-off-by: Ingo Molnar
09 Mar, 2015
4 commits
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Export context_tracking_user_enter/exit so it can be used by KVM.
Reviewed-by: Paul E. McKenney
Signed-off-by: Rik van Riel
Cc: Paul E. McKenney
Cc: Andy Lutomirski
Cc: Will deacon
Cc: Marcelo Tosatti
Cc: Christian Borntraeger
Cc: Luiz Capitulino
Cc: Paolo Bonzini
Signed-off-by: Frederic Weisbecker -
Only run vtime_user_enter, vtime_user_exit, and the user enter & exit
trace points when we are entering or exiting user state, respectively.The KVM code in guest_enter and guest_exit already take care of calling
vtime_guest_enter and vtime_guest_exit, respectively.The RCU code only distinguishes between "idle" and "not idle or kernel".
There should be no need to add an additional (unused) state there.Reviewed-by: Paul E. McKenney
Signed-off-by: Rik van Riel
Cc: Paul E. McKenney
Cc: Andy Lutomirski
Cc: Will deacon
Cc: Marcelo Tosatti
Cc: Christian Borntraeger
Cc: Luiz Capitulino
Cc: Paolo Bonzini
Signed-off-by: Frederic Weisbecker -
Generalize the context tracking APIs to support various nature of
contexts. This is performed by splitting out the mechanism from
context_tracking_user_enter and context_tracking_user_exit into
context_tracking_enter and context_tracking_exit.The nature of the context we track is now detailed in a ctx_state
parameter pushed to these APIs, allowing the same functions to not just
track kernel <> user space switching, but also kernel <> guest transitions.But leave the old functions in order to avoid breaking ARM, which calls
these functions from assembler code, and cannot easily use C enum
parameters.Reviewed-by: Paul E. McKenney
Signed-off-by: Rik van Riel
Cc: Paul E. McKenney
Cc: Andy Lutomirski
Cc: Will deacon
Cc: Marcelo Tosatti
Cc: Christian Borntraeger
Cc: Luiz Capitulino
Cc: Paolo Bonzini
Signed-off-by: Frederic Weisbecker -
Current context tracking symbols are designed to express living state.
As such they are prefixed with "IN_": IN_USER, IN_KERNEL.Now we are going to use these symbols to also express state transitions
such as context_tracking_enter(IN_USER) or context_tracking_exit(IN_USER).
But while the "IN_" prefix works well to express entering a context, it's
confusing to depict a context exit: context_tracking_exit(IN_USER)
could mean two things:
1) We are exiting the current context to enter user context.
2) We are exiting the user context
We want 2) but the reviewer may be confused and understand 1)So lets disambiguate these symbols and rename them to CONTEXT_USER and
CONTEXT_KERNEL.Acked-by: Rik van Riel
Cc: Paul E. McKenney
Cc: Andy Lutomirski
Cc: Will deacon
Cc: Marcelo Tosatti
Cc: Christian Borntraeger
Cc: Luiz Capitulino
Cc: Paolo Bonzini
Signed-off-by: Frederic Weisbecker
28 Oct, 2014
1 commit
-
preempt_schedule_context() does preempt_enable_notrace() at the end
and this can call the same function again; exception_exit() is heavy
and it is quite possible that need-resched is true again.1. Change this code to dec preempt_count() and check need_resched()
by hand.2. As Linus suggested, we can use the PREEMPT_ACTIVE bit and avoid
the enable/disable dance around __schedule(). But in this case
we need to move into sched/core.c.3. Cosmetic, but x86 forgets to declare this function. This doesn't
really matter because it is only called by asm helpers, still it
make sense to add the declaration into asm/preempt.h to match
preempt_schedule().Reported-by: Sasha Levin
Signed-off-by: Oleg Nesterov
Signed-off-by: Peter Zijlstra (Intel)
Cc: Alexander Graf
Cc: Andrew Morton
Cc: Christoph Lameter
Cc: Linus Torvalds
Cc: Masami Hiramatsu
Cc: Steven Rostedt
Cc: Peter Anvin
Cc: Andy Lutomirski
Cc: Denys Vlasenko
Cc: Chuck Ebbert
Cc: Frederic Weisbecker
Link: http://lkml.kernel.org/r/20141005202322.GB27962@redhat.com
Signed-off-by: Ingo Molnar
14 Jun, 2014
1 commit
-
This essentially reverts commit:
ecd50f714c42 ("kprobes, x86: Call exception_enter after kprobes handled")
since it causes build errors with CONFIG_CONTEXT_TRACKING and
that has been made from misunderstandings;
context_track_user_*() don't involve much in interrupt context,
it just returns if in_interrupt() is true.Instead of changing the do_debug/int3(), this just adds
context_track_user_*() to kprobes blacklist, since those are
still can be called right before kprobes handles int3 and debug
exceptions, and probing those will cause an infinite loop.Reported-by: Frederic Weisbecker
Signed-off-by: Masami Hiramatsu
Cc: Borislav Petkov
Cc: Kees Cook
Cc: Jiri Kosina
Cc: Rusty Russell
Cc: Steven Rostedt
Cc: Seiji Aguchi
Cc: Andrew Morton
Cc: Kees Cook
Link: http://lkml.kernel.org/r/20140614064711.7865.45957.stgit@kbuild-fedora.novalocal
Signed-off-by: Ingo Molnar
06 May, 2014
1 commit
-
As requested by Linus add explicit __visible to the asmlinkage users.
This marks functions visible to assembler.Tree sweep for rest of tree.
Signed-off-by: Andi Kleen
Link: http://lkml.kernel.org/r/1398984278-29319-4-git-send-email-andi@firstfloor.org
Signed-off-by: H. Peter Anvin
03 Dec, 2013
1 commit
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Use a function with a meaningful name to check the global context
tracking state. static_key_false() is a bit confusing for reviewers.Signed-off-by: Frederic Weisbecker
Cc: Thomas Gleixner
Cc: Ingo Molnar
Cc: Peter Zijlstra
Cc: Oleg Nesterov
Cc: Steven Rostedt
09 Oct, 2013
1 commit
-
Merge Linux v3.12-rc4 to fix a conflict and also to refresh the tree
before applying more scheduler patches.Conflicts:
arch/avr32/include/asm/KbuildSigned-off-by: Ingo Molnar
27 Sep, 2013
1 commit
-
ad65782fba50 (context_tracking: Optimize main APIs off case
with static key) converted context tracking main APIs to inline
function and left ARM asm callers behind.This can be easily fixed by making ARM calling the post static
keys context tracking function. We just need to replicate the
static key checks there. We'll remove these later when ARM will
support the context tracking static keys.Reported-by: Guenter Roeck
Reported-by: Russell King
Signed-off-by: Frederic Weisbecker
Tested-by: Kevin Hilman
Cc: Nicolas Pitre
Cc: Anil Kumar
Cc: Tony Lindgren
Cc: Benoit Cousson
Cc: Guenter Roeck
Cc: Russell King
Cc: Kevin Hilman
25 Sep, 2013
1 commit
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Rewrite the preempt_count macros in order to extract the 3 basic
preempt_count value modifiers:__preempt_count_add()
__preempt_count_sub()and the new:
__preempt_count_dec_and_test()
And since we're at it anyway, replace the unconventional
$op_preempt_count names with the more conventional preempt_count_$op.Since these basic operators are equivalent to the previous _notrace()
variants, do away with the _notrace() versions.Signed-off-by: Peter Zijlstra
Link: http://lkml.kernel.org/n/tip-ewbpdbupy9xpsjhg960zwbv8@git.kernel.org
Signed-off-by: Ingo Molnar
14 Aug, 2013
5 commits
-
This can be useful to track all kernel/user round trips.
And it's also helpful to debug the context tracking subsystem.Signed-off-by: Frederic Weisbecker
Cc: Steven Rostedt
Cc: Paul E. McKenney
Cc: Ingo Molnar
Cc: Thomas Gleixner
Cc: Peter Zijlstra
Cc: Borislav Petkov
Cc: Li Zhong
Cc: Mike Galbraith
Cc: Kevin Hilman -
No need for syscall slowpath if no CPU is full dynticks,
rather nop this in this case.Signed-off-by: Frederic Weisbecker
Cc: Steven Rostedt
Cc: Paul E. McKenney
Cc: Ingo Molnar
Cc: Thomas Gleixner
Cc: Peter Zijlstra
Cc: Borislav Petkov
Cc: Li Zhong
Cc: Mike Galbraith
Cc: Kevin Hilman -
Optimize guest entry/exit APIs with static keys. This minimize
the overhead for those who enable CONFIG_NO_HZ_FULL without
always using it. Having no range passed to nohz_full= should
result in the probes overhead to be minimized.Signed-off-by: Frederic Weisbecker
Cc: Steven Rostedt
Cc: Paul E. McKenney
Cc: Ingo Molnar
Cc: Thomas Gleixner
Cc: Peter Zijlstra
Cc: Borislav Petkov
Cc: Li Zhong
Cc: Mike Galbraith
Cc: Kevin Hilman -
Optimize user and exception entry/exit APIs with static
keys. This minimize the overhead for those who enable
CONFIG_NO_HZ_FULL without always using it. Having no range
passed to nohz_full= should result in the probes to be nopped
(at least we hope so...).If this proves not be enough in the long term, we'll need
to bring an exception slow path by re-routing the exception
handlers.Signed-off-by: Frederic Weisbecker
Cc: Steven Rostedt
Cc: Paul E. McKenney
Cc: Ingo Molnar
Cc: Thomas Gleixner
Cc: Peter Zijlstra
Cc: Borislav Petkov
Cc: Li Zhong
Cc: Mike Galbraith
Cc: Kevin Hilman -
Prepare for using a static key in the context tracking subsystem.
This will help optimizing the off case on its many users:* user_enter, user_exit, exception_enter, exception_exit, guest_enter,
guest_exit, vtime_*()Signed-off-by: Frederic Weisbecker
Cc: Steven Rostedt
Cc: Paul E. McKenney
Cc: Ingo Molnar
Cc: Thomas Gleixner
Cc: Peter Zijlstra
Cc: Borislav Petkov
Cc: Li Zhong
Cc: Mike Galbraith
Cc: Kevin Hilman
13 Aug, 2013
4 commits
-
The context tracking subsystem has the ability to selectively
enable the tracking on any defined subset of CPU. This means that
we can define a CPU range that doesn't run the context tracking
and another range that does.Now what we want in practice is to enable the tracking on full
dynticks CPUs only. In order to perform this, we just need to pass
our full dynticks CPU range selection from the full dynticks
subsystem to the context tracking.This way we can spare the overhead of RCU user extended quiescent
state and vtime maintainance on the CPUs that are outside the
full dynticks range. Just keep in mind the raw context tracking
itself is still necessary everywhere.Signed-off-by: Frederic Weisbecker
Cc: Steven Rostedt
Cc: Paul E. McKenney
Cc: Ingo Molnar
Cc: Thomas Gleixner
Cc: Peter Zijlstra
Cc: Borislav Petkov
Cc: Li Zhong
Cc: Mike Galbraith
Cc: Kevin Hilman -
As long as the context tracking is enabled on any CPU, even
a single one, all other CPUs need to keep track of their
user kernel boundaries cross as well.This is because a task can sleep while servicing an exception
that happened in the kernel or in userspace. Then when the task
eventually wakes up and return from the exception, the CPU needs
to know if we resume in userspace or in the kernel. exception_exit()
get this information from exception_enter() that saved the previous
state.If the CPU where the exception happened didn't keep track of
these informations, exception_exit() doesn't know which state
tracking to restore on the CPU where the task got migrated
and we may return to userspace with the context tracking
subsystem thinking that we are in kernel mode.This can be fixed in the long term if we move our context tracking
probes on very low level arch fast path user kernel boundary,
although even that is worrisome as an exception can still happen
in the few instructions between the probe and the actual iret.Also we are not yet ready to set these probes in the fast path given
the potential overhead problem it induces.So let's fix this by always enable context tracking even on CPUs
that are not in the full dynticks range. OTOH we can spare the
rcu_user_*() and vtime_user_*() calls there because the tick runs
on these CPUs and we can handle RCU state machine and cputime
accounting through it.Signed-off-by: Frederic Weisbecker
Cc: Steven Rostedt
Cc: Paul E. McKenney
Cc: Ingo Molnar
Cc: Thomas Gleixner
Cc: Peter Zijlstra
Cc: Borislav Petkov
Cc: Li Zhong
Cc: Mike Galbraith
Cc: Kevin Hilman -
1) If context tracking is enabled with native vtime accounting (which
combo is useless except for dev testing), we call vtime_guest_enter()
and vtime_guest_exit() on host guest switches. But those are stubs
in this configurations. As a result, cputime is not correctly flushed
on kvm context switches.2) If context tracking runs but is disabled on some CPUs, those
CPUs end up calling __guest_enter/__guest_exit which in turn
call vtime_account_system(). We don't want to call this because we
run in tick based accounting for these CPUs.Refactor the guest_enter/guest_exit code such that all combinations
finally work.Signed-off-by: Frederic Weisbecker
Cc: Steven Rostedt
Cc: Paul E. McKenney
Cc: Ingo Molnar
Cc: Thomas Gleixner
Cc: Peter Zijlstra
Cc: Borislav Petkov
Cc: Li Zhong
Cc: Mike Galbraith
Cc: Kevin Hilman -
preempt_schedule() and preempt_schedule_context() open
code their preemptability checks.Use the standard API instead for consolidation.
Signed-off-by: Frederic Weisbecker
Cc: Ingo Molnar
Cc: Li Zhong
Cc: Paul E. McKenney
Cc: Peter Zijlstra
Cc: Steven Rostedt
Cc: Thomas Gleixner
Cc: Borislav Petkov
Cc: Alex Shi
Cc: Paul Turner
Cc: Mike Galbraith
Cc: Vincent Guittot
21 Jun, 2013
1 commit
-
Pull scheduler fixes from Ingo Molnar:
"Two smaller fixes - plus a context tracking tracing fix that is a bit
bigger"* 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
tracing/context-tracking: Add preempt_schedule_context() for tracing
sched: Fix clear NOHZ_BALANCE_KICK
sched/x86: Construct all sibling maps if smt
19 Jun, 2013
1 commit
-
Dave Jones hit the following bug report:
===============================
[ INFO: suspicious RCU usage. ]
3.10.0-rc2+ #1 Not tainted
-------------------------------
include/linux/rcupdate.h:771 rcu_read_lock() used illegally while idle!
other info that might help us debug this:
RCU used illegally from idle CPU! rcu_scheduler_active = 1, debug_locks = 0
RCU used illegally from extended quiescent state!
2 locks held by cc1/63645:
#0: (&rq->lock){-.-.-.}, at: [] __schedule+0xed/0x9b0
#1: (rcu_read_lock){.+.+..}, at: [] cpuacct_charge+0x5/0x1f0CPU: 1 PID: 63645 Comm: cc1 Not tainted 3.10.0-rc2+ #1 [loadavg: 40.57 27.55 13.39 25/277 64369]
Hardware name: Gigabyte Technology Co., Ltd. GA-MA78GM-S2H/GA-MA78GM-S2H, BIOS F12a 04/23/2010
0000000000000000 ffff88010f78fcf8 ffffffff816ae383 ffff88010f78fd28
ffffffff810b698d ffff88011c092548 000000000023d073 ffff88011c092500
0000000000000001 ffff88010f78fd60 ffffffff8109d7c5 ffffffff8109d645
Call Trace:
[] dump_stack+0x19/0x1b
[] lockdep_rcu_suspicious+0xfd/0x130
[] cpuacct_charge+0x185/0x1f0
[] ? cpuacct_charge+0x5/0x1f0
[] update_curr+0xec/0x240
[] put_prev_task_fair+0x228/0x480
[] __schedule+0x161/0x9b0
[] preempt_schedule+0x51/0x80
[] ? __cond_resched_softirq+0x60/0x60
[] ? retint_careful+0x12/0x2e
[] ftrace_ops_control_func+0x1dc/0x210
[] ftrace_call+0x5/0x2f
[] ? retint_careful+0xb/0x2e
[] ? schedule_user+0x5/0x70
[] ? schedule_user+0x5/0x70
[] ? retint_careful+0x12/0x2e
------------[ cut here ]------------What happened was that the function tracer traced the schedule_user() code
that tells RCU that the system is coming back from userspace, and to
add the CPU back to the RCU monitoring.Because the function tracer does a preempt_disable/enable_notrace() calls
the preempt_enable_notrace() checks the NEED_RESCHED flag. If it is set,
then preempt_schedule() is called. But this is called before the user_exit()
function can inform the kernel that the CPU is no longer in user mode and
needs to be accounted for by RCU.The fix is to create a new preempt_schedule_context() that checks if
the kernel is still in user mode and if so to switch it to kernel mode
before calling schedule. It also switches back to user mode coming back
from schedule in need be.The only user of this currently is the preempt_enable_notrace(), which is
only used by the tracing subsystem.Signed-off-by: Steven Rostedt
Signed-off-by: Peter Zijlstra
Link: http://lkml.kernel.org/r/1369423420.6828.226.camel@gandalf.local.home
Signed-off-by: Ingo Molnar
31 May, 2013
1 commit
-
The kvm_host.h header file doesn't handle well
inclusion when archs don't support KVM.This results in build crashes for such archs when they
want to implement context tracking because this subsystem
includes kvm_host.h in order to implement the
guest_enter/exit APIs but it doesn't handle KVM off case.To fix this, move the guest_enter()/guest_exit()
declarations and generic implementation to the context
tracking headers. These generic APIs actually belong to
this subsystem, besides other domains boundary tracking
like user_enter() et al.KVM now properly becomes a user of this library, not the
other buggy way around.Reported-by: Kevin Hilman
Reviewed-by: Kevin Hilman
Tested-by: Kevin Hilman
Signed-off-by: Frederic Weisbecker
Cc: Steven Rostedt
Cc: Paul E. McKenney
Cc: Thomas Gleixner
Cc: Peter Zijlstra
Cc: Kevin Hilman
Cc: Marcelo Tosatti
Cc: Gleb Natapov
Signed-off-by: Ingo Molnar
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.
28 Jan, 2013
2 commits
-
While remotely reading the cputime of a task running in a
full dynticks CPU, the values stored in utime/stime fields
of struct task_struct may be stale. Its values may be those
of the last kernel user transition time snapshot and
we need to add the tickless time spent since this snapshot.To fix this, flush the cputime of the dynticks CPUs on
kernel user transition and record the time / context
where we did this. Then on top of this snapshot and the current
time, perform the fixup on the reader side from task_times()
accessors.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
[fixed kvm module related build errors]
Signed-off-by: Sedat Dilek -
If we want to stop the tick further idle, we need to be
able to account the cputime without using the tick.Virtual based cputime accounting solves that problem by
hooking into kernel/user boundaries.However implementing CONFIG_VIRT_CPU_ACCOUNTING require
low level hooks and involves more overhead. But we already
have a generic context tracking subsystem that is required
for RCU needs by archs which plan to shut down the tick
outside idle.This patch implements a generic virtual based cputime
accounting that relies on these generic kernel/user hooks.There are some upsides of doing this:
- This requires no arch code to implement CONFIG_VIRT_CPU_ACCOUNTING
if context tracking is already built (already necessary for RCU in full
tickless mode).- We can rely on the generic context tracking subsystem to dynamically
(de)activate the hooks, so that we can switch anytime between virtual
and tick based accounting. This way we don't have the overhead
of the virtual accounting when the tick is running periodically.And one downside:
- There is probably more overhead than a native virtual based cputime
accounting. But this relies on hooks that are already set anyway.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
27 Jan, 2013
2 commits
-
This subsystem lacks many explanations on its purpose and
design. Add these missing comments.v4: Document function parameter to be more kernel-doc
friendly, as per Namhyung suggestion.Reported-by: Andrew Morton
Signed-off-by: Frederic Weisbecker
Cc: Alessio Igor Bogani
Cc: Andrew Morton
Cc: Chris Metcalf
Cc: Christoph Lameter
Cc: Geoff Levand
Cc: Gilad Ben Yossef
Cc: Hakan Akkan
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
Signed-off-by: Paul E. McKenney -
Export the context state: whether we run in user / kernel
from the context tracking subsystem point of view.This is going to be used by the generic virtual cputime
accounting subsystem that is needed to implement the full
dynticks.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
01 Dec, 2012
1 commit
-
Create a new subsystem that probes on kernel boundaries
to keep track of the transitions between level contexts
with two basic initial contexts: user or kernel.This is an abstraction of some RCU code that use such tracking
to implement its userspace extended quiescent state.We need to pull this up from RCU into this new level of indirection
because this tracking is also going to be used to implement an "on
demand" generic virtual cputime accounting. A necessary step to
shutdown the tick while still accounting the cputime.Signed-off-by: Frederic Weisbecker
Cc: Andrew Morton
Cc: H. Peter Anvin
Cc: Ingo Molnar
Cc: Paul E. McKenney
Cc: Peter Zijlstra
Cc: Steven Rostedt
Cc: Thomas Gleixner
Cc: Li Zhong
Cc: Gilad Ben-Yossef
Reviewed-by: Steven Rostedt
[ paulmck: fix whitespace error and email address. ]
Signed-off-by: Paul E. McKenney