| Message ID | 20191218182607.21607-6-ionela.voinescu@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | arm64: ARMv8.4 Activity Monitors support | expand |
On Wed, Dec 18, 2019 at 06:26:06PM +0000, Ionela Voinescu wrote: > To be noted that this patch is a temporary one. It introduces the > interface added by the patches at [1] to allow update of the frequency > invariance scale factor based on counters. If [1] is merged there is > not need for this patch. > > For platforms that support counters (x86 - APERF/MPERF, arm64 - AMU > counters) the frequency invariance correction factor can be obtained > using a core counter and a fixed counter to get information on the > performance (frequency based only) obtained in a period of time. This > will more accurately reflect the actual current frequency of the CPU, > compared with the alternative implementation that reflects the request > of a performance level from the OS through the cpufreq framework > (arch_set_freq_scale). > > Therefore, introduce an interface - arch_scale_freq_tick, to be > implemented by each architecture and called for each CPU on the tick > to update the scale factor based on the delta in the counter values, > if counter support is present on the CPU. > > Either because reading counters is expensive or because reading > counters from remote CPUs is not possible or is expensive, only > update the counter based frequency scale factor on the tick for > now. A tick based update will definitely be necessary either due to > it being the only point of update for certain architectures or in > order to cache the counter values for a particular CPU, if a > further update from that CPU is not possible. > > [1] > https://lore.kernel.org/lkml/20191113124654.18122-1-ggherdovich@suse.cz/ FWIW, those patches just landed in tip/sched/core
On Wednesday 29 Jan 2020 at 20:37:41 (+0100), Peter Zijlstra wrote: > On Wed, Dec 18, 2019 at 06:26:06PM +0000, Ionela Voinescu wrote: > > To be noted that this patch is a temporary one. It introduces the > > interface added by the patches at [1] to allow update of the frequency > > invariance scale factor based on counters. If [1] is merged there is > > not need for this patch. > > > > For platforms that support counters (x86 - APERF/MPERF, arm64 - AMU > > counters) the frequency invariance correction factor can be obtained > > using a core counter and a fixed counter to get information on the > > performance (frequency based only) obtained in a period of time. This > > will more accurately reflect the actual current frequency of the CPU, > > compared with the alternative implementation that reflects the request > > of a performance level from the OS through the cpufreq framework > > (arch_set_freq_scale). > > > > Therefore, introduce an interface - arch_scale_freq_tick, to be > > implemented by each architecture and called for each CPU on the tick > > to update the scale factor based on the delta in the counter values, > > if counter support is present on the CPU. > > > > Either because reading counters is expensive or because reading > > counters from remote CPUs is not possible or is expensive, only > > update the counter based frequency scale factor on the tick for > > now. A tick based update will definitely be necessary either due to > > it being the only point of update for certain architectures or in > > order to cache the counter values for a particular CPU, if a > > further update from that CPU is not possible. > > > > [1] > > https://lore.kernel.org/lkml/20191113124654.18122-1-ggherdovich@suse.cz/ > > FWIW, those patches just landed in tip/sched/core Thanks, Peter, I'll drop this one next time around. Ionela.
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 90e4b00ace89..e0b70b9fb5cc 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -3594,6 +3594,7 @@ void scheduler_tick(void) struct task_struct *curr = rq->curr; struct rq_flags rf; + arch_scale_freq_tick(); sched_clock_tick(); rq_lock(rq, &rf); diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 280a3c735935..afdafcf7f9da 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -1771,6 +1771,13 @@ static inline void set_next_task(struct rq *rq, struct task_struct *next) next->sched_class->set_next_task(rq, next, false); } +#ifndef arch_scale_freq_tick +static __always_inline +void arch_scale_freq_tick(void) +{ +} +#endif + #ifdef CONFIG_SMP #define sched_class_highest (&stop_sched_class) #else
To be noted that this patch is a temporary one. It introduces the interface added by the patches at [1] to allow update of the frequency invariance scale factor based on counters. If [1] is merged there is not need for this patch. For platforms that support counters (x86 - APERF/MPERF, arm64 - AMU counters) the frequency invariance correction factor can be obtained using a core counter and a fixed counter to get information on the performance (frequency based only) obtained in a period of time. This will more accurately reflect the actual current frequency of the CPU, compared with the alternative implementation that reflects the request of a performance level from the OS through the cpufreq framework (arch_set_freq_scale). Therefore, introduce an interface - arch_scale_freq_tick, to be implemented by each architecture and called for each CPU on the tick to update the scale factor based on the delta in the counter values, if counter support is present on the CPU. Either because reading counters is expensive or because reading counters from remote CPUs is not possible or is expensive, only update the counter based frequency scale factor on the tick for now. A tick based update will definitely be necessary either due to it being the only point of update for certain architectures or in order to cache the counter values for a particular CPU, if a further update from that CPU is not possible. [1] https://lore.kernel.org/lkml/20191113124654.18122-1-ggherdovich@suse.cz/ Suggested-by: Peter Zijlstra <peterz@infradead.org> Suggested-by: Giovanni Gherdovich <ggherdovich@suse.cz> Signed-off-by: Ionela Voinescu <ionela.voinescu@arm.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Juri Lelli <juri.lelli@redhat.com> Cc: Vincent Guittot <vincent.guittot@linaro.org> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com> --- kernel/sched/core.c | 1 + kernel/sched/sched.h | 7 +++++++ 2 files changed, 8 insertions(+)