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Date: Tue, 2 Aug 2016 15:02:45 -0700 From: Steve Muckle <steve.muckle@...aro.org> To: "Rafael J. Wysocki" <rafael@...nel.org> Cc: Steve Muckle <steve.muckle@...aro.org>, "Rafael J. Wysocki" <rjw@...ysocki.net>, Linux PM list <linux-pm@...r.kernel.org>, Peter Zijlstra <peterz@...radead.org>, Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>, Viresh Kumar <viresh.kumar@...aro.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Juri Lelli <juri.lelli@....com>, Ingo Molnar <mingo@...nel.org> Subject: Re: [RFC][PATCH 5/7] cpufreq / sched: UUF_IO flag to indicate iowait condition On Tue, Aug 02, 2016 at 03:37:02AM +0200, Rafael J. Wysocki wrote: > On Tue, Aug 2, 2016 at 3:22 AM, Steve Muckle <steve.muckle@...aro.org> wrote: > > On Mon, Aug 01, 2016 at 01:37:23AM +0200, Rafael J. Wysocki wrote: > > ... > >> For this purpose, define a new cpufreq_update_util() flag > >> UUF_IO and modify enqueue_task_fair() to pass that flag to > >> cpufreq_update_util() in the in_iowait case. That generally > >> requires cpufreq_update_util() to be called directly from there, > >> because update_load_avg() is not likely to be invoked in that > >> case. > > > > I didn't follow why the cpufreq hook won't likely be called if > > in_iowait is set? AFAICS update_load_avg() gets called in the second loop > > and calls update_cfs_rq_load_avg (triggers the hook). > > In practice it turns out that in the majority of cases when in_iowait > is set the second loop will not run. My understanding of enqueue_task_fair() is that the first loop walks up the portion of the sched_entity hierarchy that needs to be enqueued, and the second loop updates the rest of the hierarchy that was already enqueued. Even if the se corresponding to the root cfs_rq needs to be enqueued (meaning the whole hierarchy is traversed in the first loop and the second loop does nothing), enqueue_entity() on the root cfs_rq should result in the cpufreq hook being called, via enqueue_entity() -> enqueue_entity_load_avg() -> update_cfs_rq_load_avg(). I'll keep looking to see if I've misunderstood something in here. thanks, Steve
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