Messages in this thread | ![/](/images/icornerl.gif) | | From | "Joel Fernandes (Google)" <> | Date | Wed, 26 Jul 2017 22:34:58 -0700 | Subject | Re: [Eas-dev] [PATCH V4 1/3] sched: cpufreq: Allow remote cpufreq callbacks |
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Hi Viresh,
On Wed, Jul 26, 2017 at 2:22 AM, Viresh Kumar <viresh.kumar@linaro.org> wrote: > We do not call cpufreq callbacks from scheduler core for remote > (non-local) CPUs currently. But there are cases where such remote > callbacks are useful, specially in the case of shared cpufreq policies. > > This patch updates the scheduler core to call the cpufreq callbacks for > remote CPUs as well. > > For now, all the registered utilization update callbacks are updated to > return early if remote callback is detected. That is, this patch just > moves the decision making down in the hierarchy. > > Later patches would enable remote callbacks for shared policies. > > Based on initial work from Steve Muckle. > > Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> <snip> > --- a/kernel/sched/cpufreq_schedutil.c > +++ b/kernel/sched/cpufreq_schedutil.c > @@ -72,10 +72,15 @@ static DEFINE_PER_CPU(struct sugov_cpu, sugov_cpu); > > /************************ Governor internals ***********************/ > > -static bool sugov_should_update_freq(struct sugov_policy *sg_policy, u64 time) > +static bool sugov_should_update_freq(struct sugov_policy *sg_policy, u64 time, > + int target_cpu) > { > s64 delta_ns; > > + /* Don't allow remote callbacks */ > + if (smp_processor_id() != target_cpu) > + return false; > + > if (sg_policy->work_in_progress) > return false; > > @@ -221,7 +226,7 @@ static void sugov_update_single(struct update_util_data *hook, u64 time, > sugov_set_iowait_boost(sg_cpu, time, flags); > sg_cpu->last_update = time; > > - if (!sugov_should_update_freq(sg_policy, time)) > + if (!sugov_should_update_freq(sg_policy, time, hook->cpu)) > return;
Since with the remote callbacks now possible, isn't it unsafe to modify sg_cpu and sg_policy structures without a lock in sugov_update_single?
Unlike sugov_update_shared, we don't acquire any lock in sugov_update_single before updating these structures. Did I miss something?
thanks,
-Joel
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