Messages in this thread | | | From | "Rafael J. Wysocki" <> | Date | Tue, 12 Nov 2019 09:51:46 +0100 | Subject | Re: [RFC PATCH RESEND] cpuidle: undelaying cpuidle in dpm_{suspend|resume}() |
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On Tue, Nov 12, 2019 at 6:10 AM Ikjoon Jang <ikjn@chromium.org> wrote: > > On Fri, Nov 8, 2019 at 7:22 PM Rafael J. Wysocki <rjw@rjwysocki.net> wrote: > > > > On Wednesday, October 30, 2019 3:21:05 AM CET Ikjoon Jang wrote: > > > cpuidle is paused only during dpm_suspend_noirq() ~ dpm_resume_noirq(). > > > But some device drivers need random sized IOs in dpm_{suspend|resume}() > > > stage (e.g. re-downloading firmware in resume). > > > And with such a device, cpuidle's latencies could be critical to > > > response time of system suspend/resume. > > > > > > To minimize those latencies, we could apply pm_qos to such device drivers, > > > but simply undelaying cpuidle from dpm_suspend_noirq() to dpm suspend() > > > seems no harm. > > > > While the patch is generally acceptable, the changelog is not. > > > > First, what does "undelying" mean? > > You're right, that should be fixed, > actually I used 'undelaying' from commit: 8651f97bd951d > (PM / cpuidle: System resume hang fix with cpuidle), > when the first time cpuidle_{pause|resume} is introduced: > > "Since we are dealing with drivers it seems best to call this function > during dpm_suspend(). Delaying the call till dpm_suspend_noirq() does > no harm, as long as it is before cpu_hotplug_begin() to avoid race > conditions with cpu hotpulg operations." > > Delaying does no harm, but I think that there had been no specific > reason of this > delay from the beginning. Undelaying does no harm too.
I see.
It would be good to mention commit 8651f97bd951d in the changelog. And while "delaying" is a proper word in English, "undelaying" isn't AFAICS, so maybe say "avoid delaying" or something to that effect instead.
> > > > Second, you seem to be talking about the cases in which exit latencies of > > idle states are not small relative to the system suspend/resume time, so > > without any specific examples this is not really convincing. > > > > Also, potentially, there is another reason to make this change, which is > > that on some systems i2c (or similar) controllers may be requisite for > > idle state entry and exit, so it may make sense in general to prevent > > cpuidle from being used over the entire suspend and resume of the > > system. However, without any example of a system in which that matters > > it still is not convincing enough IMO. > > > > Currently I've got only one specific device for examples. > Maybe this patch needs more generalized examples for applying to all > other machines.
One example would be enough, but please provide it in the changelog of the patch.
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