On Wed, Aug 3, 2016 at 12:02 AM, Steve Muckle <[email protected]> wrote: > 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 <[email protected]> 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().
But then it's rather difficult to pass the IO flag to this one, isn't it? Essentially, the problem is to pass "IO" to cpufreq_update_util() when p->in_iowait is set. If you can find a clever way to do it without adding an extra call site, that's fine by me, but in any case the extra cpufreq_update_util() invocation should not be too expensive. Thanks, Rafael
