Hi, On 30/11/17 11:47, Patrick Bellasi wrote: > In system where multiple CPUs shares the same frequency domain a small > workload on a CPU can still be subject to frequency spikes, generated by > the activation of the sugov's kthread. > > Since the sugov kthread is a special RT task, which goal is just that to > activate a frequency transition, it does not make sense for it to bias > the schedutil's frequency selection policy. > > This patch exploits the information related to the current task to silently > ignore cpufreq_update_this_cpu() calls, coming from the RT scheduler, while > the sugov kthread is running. > > Signed-off-by: Patrick Bellasi <patrick.bell...@arm.com> > Reviewed-by: Dietmar Eggemann <dietmar.eggem...@arm.com> > Cc: Ingo Molnar <mi...@redhat.com> > Cc: Peter Zijlstra <pet...@infradead.org> > Cc: Rafael J. Wysocki <rafael.j.wyso...@intel.com> > Cc: Viresh Kumar <viresh.ku...@linaro.org> > Cc: linux-kernel@vger.kernel.org > Cc: linux...@vger.kernel.org > > --- > Changes from v2: > - rebased on v4.15-rc1 > - moved at the end of the stack since considered more controversial > Changes from v1: > - move check before policy spinlock (JuriL) > > Change-Id: I4d749458229b6496dd24a8c357be42cd35a739fd > --- > kernel/sched/cpufreq_schedutil.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/kernel/sched/cpufreq_schedutil.c > b/kernel/sched/cpufreq_schedutil.c > index 3eea8884e61b..a93ad5b0c40d 100644 > --- a/kernel/sched/cpufreq_schedutil.c > +++ b/kernel/sched/cpufreq_schedutil.c > @@ -270,6 +270,10 @@ static void sugov_update_single(struct update_util_data > *hook, u64 time, > bool rt_mode; > bool busy; > > + /* Skip updates generated by sugov kthreads */ > + if (unlikely(current == sg_policy->thread)) > + return; > + > sugov_set_iowait_boost(sg_cpu, time, flags); > sg_cpu->last_update = time; > > @@ -356,6 +360,10 @@ static void sugov_update_shared(struct update_util_data > *hook, u64 time, > unsigned int next_f; > bool rt_mode; > > + /* Skip updates generated by sugov kthreads */ > + if (unlikely(current == sg_policy->thread)) > + return; > + > raw_spin_lock(&sg_policy->update_lock); > > sugov_get_util(&util, &max, sg_cpu->cpu);
If the DL changes (which I shall post again as soon as tip/sched/core is bumped up to 4.15-rc1) get in first, this is going to be useless (as the DL kthread gets ignored by the scheduling class itself). But, this looks good to me "in the meantime". Reviewed-by: Juri Lelli <juri.le...@redhat.com> Best, Juri
