Messages in this thread | | | From | "Rafael J. Wysocki" <> | Subject | Re: [BUG] schedutil governor produces regular max freq spikes because of lockup detector watchdog threads | Date | Mon, 08 Jan 2018 14:10:56 +0100 |
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On Monday, January 8, 2018 5:01:21 AM CET Viresh Kumar wrote: > On 05-01-18, 23:18, Rafael J. Wysocki wrote: > > On Fri, Jan 5, 2018 at 9:37 PM, Leonard Crestez <leonard.crestez@nxp.com> wrote: > > > Hello, > > > > > > When using the schedutil governor together with the softlockup detector > > > all CPUs go to their maximum frequency on a regular basis. This seems > > > to be because the watchdog creates a RT thread on each CPU and this > > > causes regular kicks with: > > > > > > cpufreq_update_this_cpu(rq, SCHED_CPUFREQ_RT); > > > > > > The schedutil governor responds to this by immediately setting the > > > maximum cpu frequency, this is very undesirable. > > > > > > The issue can be fixed by this patch from android: > > > https://patchwork.kernel.org/patch/9301909/ > > > > > > The patch stalled in a long discussion about how it's difficult for > > > cpufreq to deal with RT and how some RT users might just disable > > > cpufreq. It is indeed hard but if the system experiences regular power > > > kicks from a common debug feature they will end up disabling schedutil > > > instead. > > > > They are basically free to use the other governors instead if they prefer them. > > > > > No other governors behave this way, > > > > Because they work differently overall. > > > > > perhaps the current behavior should be considered a bug in schedutil. > > > > > > That patch now has conflicts with latest upstream. Perhaps a modified > > > variant should be reconsidered for inclusion, or is there some other > > > solution pending? > > > > Patrick has a series of patches dealing with this problem area AFAICS, > > but we are currently integrating material from Juri related to > > deadline tasks. > > I am not sure if Patrick's patches would solve this problem at all as > we still go to max for RT and the RT task is created from the > softlockup detector somehow. > > One way to fix that can be to use DL for the softlockup detector as > after Juri's patches we don't always go to max for DL. > > On the other side, AFAIR, Peter was very clear during the previous LPC > that it doesn't make sense to use rt-avg as the above patch suggests.
Right.
Why does the softlockup watchdog use RT tasks in the first place?
Thanks, Rafael
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