| Message ID | CAEi0qNnYANJ9qNAnh3H4F5igXvHhT8ujoVH3JjMgr_1aBvvcRg@mail.gmail.com (mailing list archive) |
|---|---|
| State | Not Applicable, archived |
| Headers | show |
On 26-07-17, 23:13, Joel Fernandes (Google) wrote: > On Wed, Jul 26, 2017 at 10:50 PM, Viresh Kumar <viresh.kumar@linaro.org> wrote: > > On 26-07-17, 22:34, Joel Fernandes (Google) wrote: > >> On Wed, Jul 26, 2017 at 2:22 AM, Viresh Kumar <viresh.kumar@linaro.org> wrote: > >> > @@ -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? > > > > As Peter already mentioned it earlier, the callbacks are called with > > rq locks held and so sugov_update_single() wouldn't get called in > > parallel for a target CPU. > > Ah ok, I have to catch up with that discussion since I missed the > whole thing. Now that you will have me on CC, that shouldn't happen, > thanks and sorry about the noise. > > > That's the only race you were worried about ? > > Yes. So then in that case, makes sense to move raw_spin_lock in > sugov_update_shared further down? (Just discussing, this point is > independent of your patch), Something like: Even that was discussed tomorrow with Peter :) No it wouldn't work because sg_cpu->util we are updating here may be getting read from some other cpu that shares policy with sg_cpu.
On Thu, Jul 27, 2017 at 12:44:41PM +0530, Viresh Kumar wrote:
> Even that was discussed tomorrow with Peter :)
Just to clarify I don't have a time machine. That discussion was
_yesterday_,... I think :-)
On Thu, Jul 27, 2017 at 12:14 AM, Viresh Kumar <viresh.kumar@linaro.org> wrote: > On 26-07-17, 23:13, Joel Fernandes (Google) wrote: >> On Wed, Jul 26, 2017 at 10:50 PM, Viresh Kumar <viresh.kumar@linaro.org> wrote: >> > On 26-07-17, 22:34, Joel Fernandes (Google) wrote: >> >> On Wed, Jul 26, 2017 at 2:22 AM, Viresh Kumar <viresh.kumar@linaro.org> wrote: >> >> > @@ -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? >> > >> > As Peter already mentioned it earlier, the callbacks are called with >> > rq locks held and so sugov_update_single() wouldn't get called in >> > parallel for a target CPU. >> >> Ah ok, I have to catch up with that discussion since I missed the >> whole thing. Now that you will have me on CC, that shouldn't happen, >> thanks and sorry about the noise. >> >> > That's the only race you were worried about ? >> >> Yes. So then in that case, makes sense to move raw_spin_lock in >> sugov_update_shared further down? (Just discussing, this point is >> independent of your patch), Something like: > > Even that was discussed tomorrow with Peter :) > > No it wouldn't work because sg_cpu->util we are updating here may be > getting read from some other cpu that shares policy with sg_cpu. > Ok. yes you are right :) thank you Viresh and Peter for the clarification. thanks, -Joel
diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c index 622eed1b7658..9a6c12fb2c16 100644 --- a/kernel/sched/cpufreq_schedutil.c +++ b/kernel/sched/cpufreq_schedutil.c @@ -295,8 +295,6 @@ static void sugov_update_shared(struct update_util_data *hook, u64 time, sugov_get_util(&util, &max); - raw_spin_lock(&sg_policy->update_lock); - sg_cpu->util = util; sg_cpu->max = max;