linux-toradex.git/kernel/time/sched_clock.c, branch v4.10-rc7

timers, sched/clock: Clean up the code a bit

2015-03-27T07:34:01+00:00

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.asm

Cc: 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

timers, sched/clock: Avoid deadlock during read from NMI

2015-03-27T07:34:00+00:00

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

timers, sched/clock: Remove redundant notrace from update function

2015-03-27T07:33:59+00:00

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

timers, sched/clock: Remove suspend from clock_read_data()

2015-03-27T07:33:58+00:00

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

timers, sched/clock: Optimize cache line usage

2015-03-27T07:33:57+00:00

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

timers, sched/clock: Match scope of read and write seqcounts

2015-03-27T07:33:56+00:00

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

clocksource: Add 'max_cycles' to 'struct clocksource'

2015-03-12T09:16:38+00:00

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

clocksource: Simplify the logic around clocksource wrapping safety margins

2015-03-12T09:16:38+00:00

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

sched_clock: Avoid corrupting hrtimer tree during suspend

2014-07-24T10:02:49+00:00

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

sched_clock: Remove deprecated setup_sched_clock() API

2014-04-22T20:38:33+00:00

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