Messages in this thread | | | From | "Rafael J. Wysocki" <> | Date | Mon, 21 Jun 2021 16:17:59 +0200 | Subject | Re: [PATCH V3 2/3] cpufreq: intel_pstate: Migrate away from ->stop_cpu() callback |
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On Mon, Jun 21, 2021 at 5:09 AM Viresh Kumar <viresh.kumar@linaro.org> wrote: > > On 18-06-21, 14:00, Rafael J. Wysocki wrote: > > On Fri, Jun 18, 2021 at 5:22 AM Viresh Kumar <viresh.kumar@linaro.org> wrote: > > > > > > commit 367dc4aa932b ("cpufreq: Add stop CPU callback to cpufreq_driver > > > interface") added the stop_cpu() callback to allow the drivers to do > > > clean up before the CPU is completely down and its state can't be > > > modified. > > > > > > At that time the CPU hotplug framework used to call the cpufreq core's > > > registered notifier for different events like CPU_DOWN_PREPARE and > > > CPU_POST_DEAD. The stop_cpu() callback was called during the > > > CPU_DOWN_PREPARE event. > > > > > > This is no longer the case, cpuhp_cpufreq_offline() is called only once > > > by the CPU hotplug core now and we don't really need to separately > > > call stop_cpu() for cpufreq drivers. > > > > > > Migrate to using the exit() and offline() callbacks instead of > > > stop_cpu(). > > > > > > We need to clear util hook from both the callbacks, exit() and > > > offline(), since it is possible that only exit() gets called sometimes > > > (specially on errors) or both get called at other times. > > > intel_pstate_clear_update_util_hook() anyway have enough protection in > > > place if it gets called a second time and will return early then. > > > > > > Cc: Dirk Brandewie <dirk.brandewie@gmail.com> > > > Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> > > > --- > > > V2->V3: > > > - Update intel_pstate_cpu_offline() as well. > > > - Improved commit log. > > > > > > drivers/cpufreq/intel_pstate.c | 12 ++++-------- > > > 1 file changed, 4 insertions(+), 8 deletions(-) > > > > > > diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c > > > index 0e69dffd5a76..8f8a2d9d7daa 100644 > > > --- a/drivers/cpufreq/intel_pstate.c > > > +++ b/drivers/cpufreq/intel_pstate.c > > > @@ -2335,6 +2335,8 @@ static int intel_pstate_cpu_offline(struct cpufreq_policy *policy) > > > > > > pr_debug("CPU %d going offline\n", cpu->cpu); > > > > > > + intel_pstate_clear_update_util_hook(policy->cpu); > > > + > > > if (cpu->suspended) > > > return 0; > > > > > > @@ -2374,17 +2376,12 @@ static int intel_pstate_cpu_online(struct cpufreq_policy *policy) > > > return 0; > > > } > > > > > > -static void intel_pstate_stop_cpu(struct cpufreq_policy *policy) > > > -{ > > > - pr_debug("CPU %d stopping\n", policy->cpu); > > > - > > > - intel_pstate_clear_update_util_hook(policy->cpu); > > > -} > > > - > > > static int intel_pstate_cpu_exit(struct cpufreq_policy *policy) > > > { > > > pr_debug("CPU %d exiting\n", policy->cpu); > > > > > > + intel_pstate_clear_update_util_hook(policy->cpu); > > > > This change is not needed now, because ->offline always runs before > > ->exit if present. > > Not necessarily, we don't call ->offline() for many error paths in > cpufreq_online().
I guess you mean the error paths in cpufreq_offline()?
IMO this is confusing/broken, because ->offline should always be called after ->online has returned success.
> offline() only comes into play after driver is registered properly once.
The relevant intel_pstate case is a ->setpolicy driver where ->setpolicy or ->online, if successful, need to be followed by ->offline.
If ->setpolicy is successful in the cpufreq_online() path, the entire cpufreq_online() is successful and the error paths in question are not executed.
So the change I was talking about is not needed AFAICS.
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