Messages in this thread | | | From | Barry Song <> | Date | Tue, 24 Jul 2012 14:43:28 +0800 | Subject | Re: [RFC] ARM: sched_clock: update epoch_cyc on resume |
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2012/7/18 Colin Cross <ccross@android.com>: > Many clocks that are used to provide sched_clock will reset during > suspend. If read_sched_clock returns 0 after suspend, sched_clock will > appear to jump forward. This patch resets cd.epoch_cyc to the current > value of read_sched_clock during resume, which causes sched_clock() just > after suspend to return the same value as sched_clock() just before > suspend. > > In addition, during the window where epoch_ns has been updated before > suspend, but epoch_cyc has not been updated after suspend, it is unknown > whether the clock has reset or not, and sched_clock() could return a > bogus value. Add a suspended flag, and return the pre-suspend epoch_ns > value during this period.
Acked-by: Barry Song <21cnbao@gmail.com>
this patch should also fix the issue that: 1. launch some rt threads, rt threads sleep before suspend 2. repeat to suspend/resume 3. after resuming, waking up rt threads
repeat 1-3 again and again, sometimes all rt threads will hang after resuming due to wrong sched_clock will make sched_rt think rt_time is much more than rt_runtime (default 950ms in 1s). then rt threads will lost cpu timeslot to run since the 95% threshold is there.
> > This will have a side effect of causing SoCs that have clocks that > continue to count in suspend to appear to stop counting, reporting the > same sched_clock() value before and after suspend. > > Signed-off-by: Colin Cross <ccross@android.com> > --- > arch/arm/kernel/sched_clock.c | 13 +++++++++++++ > 1 files changed, 13 insertions(+), 0 deletions(-) > > diff --git a/arch/arm/kernel/sched_clock.c b/arch/arm/kernel/sched_clock.c > index 27d186a..46c7d32 100644 > --- a/arch/arm/kernel/sched_clock.c > +++ b/arch/arm/kernel/sched_clock.c > @@ -21,6 +21,7 @@ struct clock_data { > u32 epoch_cyc_copy; > u32 mult; > u32 shift; > + bool suspended; > }; > > static void sched_clock_poll(unsigned long wrap_ticks); > @@ -49,6 +50,9 @@ static unsigned long long cyc_to_sched_clock(u32 cyc, u32 mask) > u64 epoch_ns; > u32 epoch_cyc; > > + if (cd.suspended) > + return cd.epoch_ns; > + > /* > * Load the epoch_cyc and epoch_ns atomically. We do this by > * ensuring that we always write epoch_cyc, epoch_ns and > @@ -169,11 +173,20 @@ void __init sched_clock_postinit(void) > static int sched_clock_suspend(void) > { > sched_clock_poll(sched_clock_timer.data); > + cd.suspended = true; > return 0; > } > > +static void sched_clock_resume(void) > +{ > + cd.epoch_cyc = read_sched_clock(); > + cd.epoch_cyc_copy = cd.epoch_cyc; > + cd.suspended = false; > +} > + > static struct syscore_ops sched_clock_ops = { > .suspend = sched_clock_suspend, > + .resume = sched_clock_resume, > }; > > static int __init sched_clock_syscore_init(void)
-barry
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