From: "Rafael J. Wysocki" <firstname.lastname@example.org> To: Viresh Kumar <email@example.com> Cc: "Rafael J. Wysocki" <firstname.lastname@example.org>, Srinivas Pandruvada <email@example.com>, Len Brown <firstname.lastname@example.org>, Linux PM <email@example.com>, Vincent Guittot <firstname.lastname@example.org>, "v4 . 18+" <email@example.com>, Doug Smythies <firstname.lastname@example.org>, Linux Kernel Mailing List <email@example.com> Subject: Re: [PATCH V3 2/2] cpufreq: intel_pstate: Implement ->resolve_freq() Date: Tue, 6 Aug 2019 10:05:51 +0200 [thread overview] Message-ID: <CAJZ5v0hepyx_yVC=di7E6VSme4GF11p+OhQfA==1p5-FwVRM0Q@mail.gmail.com> (raw) In-Reply-To: <20190806041048.ksqs3l5bzsakaael@vireshk-i7> On Tue, Aug 6, 2019 at 6:10 AM Viresh Kumar <firstname.lastname@example.org> wrote: > > On 02-08-19, 11:28, Rafael J. Wysocki wrote: > > On Friday, August 2, 2019 11:17:55 AM CEST Rafael J. Wysocki wrote: > > > On Fri, Aug 2, 2019 at 7:44 AM Viresh Kumar <email@example.com> wrote: > > > > > > > > Intel pstate driver exposes min_perf_pct and max_perf_pct sysfs files, > > > > which can be used to force a limit on the min/max P state of the driver. > > > > Though these files eventually control the min/max frequencies that the > > > > CPUs will run at, they don't make a change to policy->min/max values. > > > > > > That's correct. > > > > > > > When the values of these files are changed (in passive mode of the > > > > driver), it leads to calling ->limits() callback of the cpufreq > > > > governors, like schedutil. On a call to it the governors shall > > > > forcefully update the frequency to come within the limits. > > > > > > OK, so the problem is that it is a bug to invoke the governor's ->limits() > > > callback without updating policy->min/max, because that's what > > > "limits" mean to the governors. > > > > > > Fair enough. > > > > AFAICS this can be addressed by adding PM QoS freq limits requests of each CPU to > > intel_pstate in the passive mode such that changing min_perf_pct or max_perf_pct > > will cause these requests to be updated. > > Right, that sounds like a good plan. > > But that will never make it to the stable kernels as there will be a > long dependency of otherwise unrelated patches to get that done. My > initial thought was to get this patch merged as it is and then later > migrate to QoS, but since this patch doesn't fix ondemand and > conservative, this patch isn't good enough as well. Right. > Maybe we should add the regular notifier based solution first, mark it > for stable kernels, and then add the QoS specific solution ? I'm not sure if -stable kernels really need a fix here. Let's just make sure that the mainline is OK and let's go straight for the final approach.
next prev parent reply other threads:[~2019-08-06 8:06 UTC|newest] Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-08-02 5:44 [PATCH V3 1/2] cpufreq: schedutil: Don't skip freq update when limits change Viresh Kumar 2019-08-02 5:44 ` [PATCH V3 2/2] cpufreq: intel_pstate: Implement ->resolve_freq() Viresh Kumar 2019-08-02 9:17 ` Rafael J. Wysocki 2019-08-02 9:28 ` Rafael J. Wysocki 2019-08-03 15:00 ` Doug Smythies 2019-08-05 8:35 ` Rafael J. Wysocki 2019-08-06 4:10 ` Viresh Kumar 2019-08-06 8:05 ` Rafael J. Wysocki [this message] 2019-08-02 9:11 ` [PATCH V3 1/2] cpufreq: schedutil: Don't skip freq update when limits change Rafael J. Wysocki 2019-08-03 0:00 ` Doug Smythies
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