27 Mar, 2015
6 commits
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Trivial cleanups, to improve the readability of the generic sched_clock() code:
- Improve and standardize comments
- Standardize the coding style
- Use vertical spacing where appropriate
- etc.No code changed:
md5:
19a053b31e0c54feaeff1492012b019a sched_clock.o.before.asm
19a053b31e0c54feaeff1492012b019a sched_clock.o.after.asmCc: Catalin Marinas
Cc: Daniel Thompson
Cc: John Stultz
Cc: Peter Zijlstra (Intel)
Cc: Peter Zijlstra
Cc: Russell King
Cc: Stephen Boyd
Cc: Thomas Gleixner
Cc: Will Deacon
Signed-off-by: Ingo Molnar -
Currently it is possible for an NMI (or FIQ on ARM) to come in
and read sched_clock() whilst update_sched_clock() has locked
the seqcount for writing. This results in the NMI handler
locking up when it calls raw_read_seqcount_begin().This patch fixes the NMI safety issues by providing banked clock
data. This is a similar approach to the one used in Thomas
Gleixner's 4396e058c52e("timekeeping: Provide fast and NMI safe
access to CLOCK_MONOTONIC").Suggested-by: Stephen Boyd
Signed-off-by: Daniel Thompson
Signed-off-by: John Stultz
Reviewed-by: Stephen Boyd
Acked-by: Peter Zijlstra (Intel)
Cc: Catalin Marinas
Cc: Peter Zijlstra
Cc: Russell King
Cc: Thomas Gleixner
Cc: Will Deacon
Link: http://lkml.kernel.org/r/1427397806-20889-6-git-send-email-john.stultz@linaro.org
Signed-off-by: Ingo Molnar -
Currently update_sched_clock() is marked as notrace but this
function is not called by ftrace. This is trivially fixed by
removing the mark up.Signed-off-by: Daniel Thompson
Signed-off-by: John Stultz
Reviewed-by: Stephen Boyd
Acked-by: Peter Zijlstra (Intel)
Cc: Catalin Marinas
Cc: Peter Zijlstra
Cc: Russell King
Cc: Thomas Gleixner
Cc: Will Deacon
Link: http://lkml.kernel.org/r/1427397806-20889-5-git-send-email-john.stultz@linaro.org
Signed-off-by: Ingo Molnar -
Currently cd.read_data.suspended is read by the hotpath function
sched_clock(). This variable need not be accessed on the
hotpath. In fact, once it is removed, we can remove the
conditional branches from sched_clock() and install a dummy
read_sched_clock function to suspend the clock.The new master copy of the function pointer
(actual_read_sched_clock) is introduced and is used for all
reads of the clock hardware except those within sched_clock
itself.Suggested-by: Thomas Gleixner
Signed-off-by: Daniel Thompson
Signed-off-by: John Stultz
Reviewed-by: Stephen Boyd
Acked-by: Peter Zijlstra (Intel)
Cc: Catalin Marinas
Cc: Peter Zijlstra
Cc: Russell King
Cc: Will Deacon
Link: http://lkml.kernel.org/r/1427397806-20889-4-git-send-email-john.stultz@linaro.org
Signed-off-by: Ingo Molnar -
Currently sched_clock(), a very hot code path, is not optimized
to minimise its cache profile. In particular:1. cd is not ____cacheline_aligned,
2. struct clock_data does not distinguish between hotpath and
coldpath data, reducing locality of reference in the hotpath,3. Some hotpath data is missing from struct clock_data and is marked
__read_mostly (which more or less guarantees it will not share a
cache line with cd).This patch corrects these problems by extracting all hotpath
data into a separate structure and using ____cacheline_aligned
to ensure the hotpath uses a single (64 byte) cache line.Signed-off-by: Daniel Thompson
Signed-off-by: John Stultz
Reviewed-by: Stephen Boyd
Acked-by: Peter Zijlstra (Intel)
Cc: Catalin Marinas
Cc: Peter Zijlstra
Cc: Russell King
Cc: Thomas Gleixner
Cc: Will Deacon
Link: http://lkml.kernel.org/r/1427397806-20889-3-git-send-email-john.stultz@linaro.org
Signed-off-by: Ingo Molnar -
Currently the scope of the raw_write_seqcount_begin/end() in
sched_clock_register() far exceeds the scope of the read section
in sched_clock(). This gives the impression of safety during
cursory review but achieves little.Note that this is likely to be a latent issue at present because
sched_clock_register() is typically called before we enable
interrupts, however the issue does risk bugs being needlessly
introduced as the code evolves.This patch fixes the problem by increasing the scope of the read
locking performed by sched_clock() to cover all data modified by
sched_clock_register.We also improve clarity by moving writes to struct clock_data
that do not impact sched_clock() outside of the critical
section.Signed-off-by: Daniel Thompson
[ Reworked it slightly to apply to tip/timers/core]
Signed-off-by: John Stultz
Reviewed-by: Stephen Boyd
Acked-by: Peter Zijlstra (Intel)
Cc: Catalin Marinas
Cc: Peter Zijlstra
Cc: Russell King
Cc: Thomas Gleixner
Cc: Will Deacon
Link: http://lkml.kernel.org/r/1427397806-20889-2-git-send-email-john.stultz@linaro.org
Signed-off-by: Ingo Molnar
12 Mar, 2015
2 commits
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In order to facilitate clocksource validation, add a
'max_cycles' field to the clocksource structure which
will hold the maximum cycle value that can safely be
multiplied without potentially causing an overflow.Signed-off-by: John Stultz
Cc: Dave Jones
Cc: Linus Torvalds
Cc: Peter Zijlstra
Cc: Prarit Bhargava
Cc: Richard Cochran
Cc: Stephen Boyd
Cc: Thomas Gleixner
Link: http://lkml.kernel.org/r/1426133800-29329-4-git-send-email-john.stultz@linaro.org
Signed-off-by: Ingo Molnar -
The clocksource logic has a number of places where we try to
include a safety margin. Most of these are 12% safety margins,
but they are inconsistently applied and sometimes are applied
on top of each other.Additionally, in the previous patch, we corrected an issue
where we unintentionally in effect created a 50% safety margin,
which these 12.5% margins where then added to.So to simplify the logic here, this patch removes the various
12.5% margins, and consolidates adding the margin in one place:
clocks_calc_max_nsecs().Additionally, Linus prefers a 50% safety margin, as it allows
bad clock values to be more easily caught. This should really
have no net effect, due to the corrected issue earlier which
caused greater then 50% margins to be used w/o issue.Signed-off-by: John Stultz
Acked-by: Stephen Boyd (for the sched_clock.c bit)
Cc: Dave Jones
Cc: Linus Torvalds
Cc: Peter Zijlstra
Cc: Prarit Bhargava
Cc: Richard Cochran
Cc: Thomas Gleixner
Link: http://lkml.kernel.org/r/1426133800-29329-3-git-send-email-john.stultz@linaro.org
Signed-off-by: Ingo Molnar
24 Jul, 2014
1 commit
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During suspend we call sched_clock_poll() to update the epoch and
accumulated time and reprogram the sched_clock_timer to fire
before the next wrap-around time. Unfortunately,
sched_clock_poll() doesn't restart the timer, instead it relies
on the hrtimer layer to do that and during suspend we aren't
calling that function from the hrtimer layer. Instead, we're
reprogramming the expires time while the hrtimer is enqueued,
which can cause the hrtimer tree to be corrupted. Furthermore, we
restart the timer during suspend but we update the epoch during
resume which seems counter-intuitive.Let's fix this by saving the accumulated state and canceling the
timer during suspend. On resume we can update the epoch and
restart the timer similar to what we would do if we were starting
the clock for the first time.Fixes: a08ca5d1089d "sched_clock: Use an hrtimer instead of timer"
Signed-off-by: Stephen Boyd
Signed-off-by: John Stultz
Link: http://lkml.kernel.org/r/1406174630-23458-1-git-send-email-john.stultz@linaro.org
Cc: Ingo Molnar
Cc: stable
Signed-off-by: Thomas Gleixner
23 Apr, 2014
1 commit
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Remove the 32-bit only setup_sched_clock() API now that all users
have been converted to the 64-bit friendly sched_clock_register().Signed-off-by: Stephen Boyd
Signed-off-by: John Stultz
20 Feb, 2014
1 commit
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The generic sched_clock registration function was previously
done lockless, due to the fact that it was expected to be called
only once. However, now there are systems that may register
multiple sched_clock sources, for which the lack of locking has
casued problems:If two sched_clock sources are registered we may end up in a
situation where a call to sched_clock() may be accessing the
epoch cycle count for the old counter and the cycle count for the
new counter. This can lead to confusing results where
sched_clock() values jump and then are reset to 0 (due to the way
the registration function forces the epoch_ns to be 0).Fix this by reorganizing the registration function to hold the
seqlock for as short a time as possible while we update the
clock_data structure for a new counter. We also put any
accumulated time into epoch_ns instead of resetting the time to
0 so that the clock doesn't reset after each successful
registration.[jstultz: Added extra context to the commit message]
Reported-by: Will Deacon
Signed-off-by: Stephen Boyd
Cc: Peter Zijlstra
Cc: Ingo Molnar
Cc: Will Deacon
Cc: Peter Zijlstra
Cc: Josh Cartwright
Link: http://lkml.kernel.org/r/1392662736-7803-2-git-send-email-john.stultz@linaro.org
Signed-off-by: John Stultz
Signed-off-by: Thomas Gleixner
12 Jan, 2014
1 commit
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Unfortunately the seqlock lockdep enablement can't be used
in sched_clock(), since the lockdep infrastructure eventually
calls into sched_clock(), which causes a deadlock.Thus, this patch changes all generic sched_clock() usage
to use the raw_* methods.Acked-by: Linus Torvalds
Reviewed-by: Stephen Boyd
Reported-by: Krzysztof Hałasa
Signed-off-by: John Stultz
Cc: Uwe Kleine-König
Cc: Willy Tarreau
Signed-off-by: Peter Zijlstra
Link: http://lkml.kernel.org/r/1388704274-5278-2-git-send-email-john.stultz@linaro.org
Signed-off-by: Ingo Molnar
10 Oct, 2013
1 commit
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Nobody is using sched_clock_func() anymore now that sched_clock
supports up to 64 bits. Remove the hook so that new code only
uses sched_clock_register().Signed-off-by: Stephen Boyd
Signed-off-by: John Stultz
31 Jul, 2013
3 commits
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The ARM architected system counter has at least 56 usable bits.
Add support for counters with more than 32 bits to the generic
sched_clock implementation so we can increase the time between
wakeups due to dealing with wrap-around on these devices while
benefiting from the irqtime accounting and suspend/resume
handling that the generic sched_clock code already has. On my
system using 56 bits over 32 bits changes the wraparound time
from a few minutes to an hour. For faster running counters (GHz
range) this is even more important because we may not be able to
execute the timer in time to deal with the wraparound if only 32
bits are used.We choose a maxsec value of 3600 seconds because we assume no
system will go idle for more than an hour. In the future we may
need to increase this value.Note: All users should switch over to the 64-bit read function so
we can remove setup_sched_clock() in favor of sched_clock_register().Cc: Russell King
Signed-off-by: Stephen Boyd
Signed-off-by: John Stultz -
In the next patch we're going to increase the number of bits that
the generic sched_clock can handle to be greater than 32. With
more than 32 bits the wraparound time can be larger than what can
fit into the units that msecs_to_jiffies takes (unsigned int).
Luckily, the wraparound is initially calculated in nanoseconds
which we can easily use with hrtimers, so switch to using an
hrtimer.Cc: Russell King
Signed-off-by: Stephen Boyd
[jstultz: Fixup hrtimer intitialization order issue]
Signed-off-by: John Stultz -
We're going to increase the cyc value to 64 bits in the near
future. Doing that is going to break the custom seqcount
implementation in the sched_clock code because 64 bit numbers
aren't guaranteed to be atomic. Replace the cyc_copy with a
seqcount to avoid this problem.Cc: Russell King
Acked-by: Will Deacon
Signed-off-by: Stephen Boyd
Signed-off-by: John Stultz
18 Jun, 2013
1 commit
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There is a small race between when the cycle count is read from
the hardware and when the epoch stabilizes. Consider this
scenario:CPU0 CPU1
---- ----
cyc = read_sched_clock()
cyc_to_sched_clock()
update_sched_clock()
...
cd.epoch_cyc = cyc;
epoch_cyc = cd.epoch_cyc;
...
epoch_ns + cyc_to_ns((cyc - epoch_cyc)The cyc on cpu0 was read before the epoch changed. But we
calculate the nanoseconds based on the new epoch by subtracting
the new epoch from the old cycle count. Since epoch is most likely
larger than the old cycle count we calculate a large number that
will be converted to nanoseconds and added to epoch_ns, causing
time to jump forward too much.Fix this problem by reading the hardware after the epoch has
stabilized.Cc: Russell King
Signed-off-by: Stephen Boyd
Signed-off-by: John Stultz
13 Jun, 2013
1 commit
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Nothing about the sched_clock implementation in the ARM port is
specific to the architecture. Generalize the code so that other
architectures can use it by selecting GENERIC_SCHED_CLOCK.Signed-off-by: Stephen Boyd
[jstultz: Merge minor collisions with other patches in my tree]
Signed-off-by: John Stultz