From: khilman@deeprootsystems•com (Kevin Hilman)
To: linux-arm-kernel@lists•infradead.org
Subject: [RFC] ARM: sched_clock: update epoch_cyc on resume
Date: Fri, 19 Oct 2012 16:58:36 -0700 [thread overview]
Message-ID: <87r4ouggk3.fsf@deeprootsystems.com> (raw)
In-Reply-To: <CAGsJ_4z_tF3LKy-vygr=kwah7q7U03Y2K2XKAkZTB1QC2pSYmw@mail.gmail.com> (Barry Song's message of "Tue, 24 Jul 2012 14:43:28 +0800")
Barry Song <21cnbao@gmail•com> writes:
> 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.
Re-visiting this in light of a related problem.
I've run into a similar issue where IRQ threads are prevented from
running during resume becase the RT throttling kicks because RT
runtime is accumulated during suspend. Using the 'needs_suspend'
version fixes this problem too.
However, because of the RT throttling issue, it seems like *all*
platforms should be using the 'needs_suspend' version always. But, as
already pointed out, that makes the timed printk output during
suspend/resume rather unhelpful.
Having to choose between useful printk times during suspend/resume and
functioning IRQ threads during suspend/resume isn't a choice I want to
make. I'd rather have both. Any ideas?
Kevin
prev parent reply other threads:[~2012-10-19 23:58 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-07-17 23:27 [RFC] ARM: sched_clock: update epoch_cyc on resume Colin Cross
2012-07-23 18:55 ` Linus Walleij
2012-07-23 19:27 ` Colin Cross
2012-07-24 0:14 ` Linus Walleij
2012-07-24 0:28 ` Colin Cross
2012-07-24 9:16 ` Bedia, Vaibhav
2012-07-27 22:23 ` Linus Walleij
2012-07-27 22:41 ` Russell King - ARM Linux
2012-07-30 12:31 ` Bedia, Vaibhav
2012-07-24 6:43 ` Barry Song
2012-10-19 23:58 ` Kevin Hilman [this message]
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