Messages in this thread | | | Date | Sun, 5 Aug 2012 02:18:33 +0200 | Subject | Re: [RFC v2] ARM: sched_clock: update epoch_cyc on resume | From | Linus Walleij <> |
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On Fri, Aug 3, 2012 at 3:28 AM, Colin Cross <ccross@android.com> wrote: > On Fri, Jul 27, 2012 at 8:30 PM, Colin Cross <ccross@android.com> wrote: >> On Fri, Jul 27, 2012 at 6:15 PM, Colin Cross <ccross@android.com> wrote: >>> That patch was merged in 3.4, and my patch is on top of it. Your >>> patch updates epoch_cyc and epoch_ns in suspend, but if the first call >>> to cyc_to_sched_clock after resume gets cyc = 0, cyc - epoch_cyc can >>> be negative, although it will be cast back to a large positive number. >>> >>> With my patch, epoch_cyc is updated in resume to whatever >>> read_sched_clock() returns, and epoch_ns is still set to the suspend >>> value, so it appears that sched_clock has not changed between >>> sched_clock_suspend and sched_clock_resume. It will work with any >>> timer behavior (reset to 0, reset to random value, or continuing >>> counting). The old setup_sched_clock function maintains the old >>> behavior to appease those who like their 32kHz sched clock to continue >>> ticking in suspend, although I think it is more correct for all sched >>> clocks to be faster than 32 kHz (when possible) and stop in suspend. >> >> I think the existing code can cause sched_clock to go backwards if the >> register read by the read function resets to 0 in suspend: >> >> In sched_clock_suspend epoch_cyc is updated to 0x00002000. >> >> The first sched_clock call after resume gets cyc = 0, returning >> epoch_ns + cyc_to_ns(0xffffe000) >> >> Later, sched_clock gets cyc = 0x5000, returning epoch_ns + >> cyc_to_ns(0x3000), which will be much smaller than the previous >> sched_clock value. > > Russell, any update on this? Should sched_clock.c handle read > functions that go backwards in suspend, or should I modify the read > function to track an offset in suspend and always return a > monotonically increasing value across suspend?
Colin, I suggest you put this into Russell's patch tracker so he can keep track of it from there.
Yours, Linus Walleij
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