| Message ID | 20221207101705.9460-1-lukasz.luba@arm.com |
|---|---|
| Headers | show |
| Series | cpufreq: schedutil: Optimize operations in hot path frequency switch | expand |
On 07-12-22, 10:17, Lukasz Luba wrote: > The max CPU capacity is the same for all CPUs sharing frequency domain > and thus 'policy' object. There is a way to avoid heavy operations > in a loop for each CPU by leveraging this knowledge. Thus, simplify > the looping code in the sugov_next_freq_shared() and drop heavy > multiplications. Instead, use simple max() to get the highest utilization > from these CPUs. This is useful for platforms with many (4 or 6) little > CPUs. > > The max CPU capacity must be fetched every time we are called, due to > difficulties during the policy setup, where we are not able to get the > normalized CPU capacity at the right time. > > The stored value in sugov_policy::max is also than used in > sugov_iowait_apply() to calculate the right boost. Thus, that field is > useful to have in that sugov_policy struct. > > Signed-off-by: Lukasz Luba <lukasz.luba@arm.com> > --- > kernel/sched/cpufreq_schedutil.c | 22 +++++++++++----------- > 1 file changed, 11 insertions(+), 11 deletions(-) Looks okay to me. Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
On Wed, 7 Dec 2022 at 11:17, Lukasz Luba <lukasz.luba@arm.com> wrote: > > The max CPU capacity is the same for all CPUs sharing frequency domain > and thus 'policy' object. There is a way to avoid heavy operations > in a loop for each CPU by leveraging this knowledge. Thus, simplify > the looping code in the sugov_next_freq_shared() and drop heavy > multiplications. Instead, use simple max() to get the highest utilization > from these CPUs. This is useful for platforms with many (4 or 6) little > CPUs. > > The max CPU capacity must be fetched every time we are called, due to > difficulties during the policy setup, where we are not able to get the > normalized CPU capacity at the right time. > > The stored value in sugov_policy::max is also than used in > sugov_iowait_apply() to calculate the right boost. Thus, that field is > useful to have in that sugov_policy struct. > > Signed-off-by: Lukasz Luba <lukasz.luba@arm.com> > --- > kernel/sched/cpufreq_schedutil.c | 22 +++++++++++----------- > 1 file changed, 11 insertions(+), 11 deletions(-) > > diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c > index c19d6de67b7a..f9881f3d9488 100644 > --- a/kernel/sched/cpufreq_schedutil.c > +++ b/kernel/sched/cpufreq_schedutil.c > @@ -158,10 +158,8 @@ static unsigned int get_next_freq(struct sugov_policy *sg_policy, > > static void sugov_get_util(struct sugov_cpu *sg_cpu) > { > - struct sugov_policy *sg_policy = sg_cpu->sg_policy; > struct rq *rq = cpu_rq(sg_cpu->cpu); > > - sg_policy->max = arch_scale_cpu_capacity(sg_cpu->cpu); > sg_cpu->bw_dl = cpu_bw_dl(rq); > sg_cpu->util = effective_cpu_util(sg_cpu->cpu, cpu_util_cfs(sg_cpu->cpu), > FREQUENCY_UTIL, NULL); > @@ -317,6 +315,8 @@ static inline void ignore_dl_rate_limit(struct sugov_cpu *sg_cpu) > static inline bool sugov_update_single_common(struct sugov_cpu *sg_cpu, > u64 time, unsigned int flags) > { > + struct sugov_policy *sg_policy = sg_cpu->sg_policy; > + > sugov_iowait_boost(sg_cpu, time, flags); > sg_cpu->last_update = time; > > @@ -325,6 +325,9 @@ static inline bool sugov_update_single_common(struct sugov_cpu *sg_cpu, > if (!sugov_should_update_freq(sg_cpu->sg_policy, time)) > return false; > > + /* Fetch the latest CPU capcity to avoid stale data */ > + sg_policy->max = arch_scale_cpu_capacity(sg_cpu->cpu); > + > sugov_get_util(sg_cpu); > sugov_iowait_apply(sg_cpu, time); > > @@ -414,25 +417,22 @@ static unsigned int sugov_next_freq_shared(struct sugov_cpu *sg_cpu, u64 time) > { > struct sugov_policy *sg_policy = sg_cpu->sg_policy; > struct cpufreq_policy *policy = sg_policy->policy; > - unsigned long util = 0, max = 1; > + unsigned long util = 0; > unsigned int j; > > + /* Fetch the latest CPU capcity to avoid stale data */ > + sg_policy->max = arch_scale_cpu_capacity(sg_cpu->cpu); > + > for_each_cpu(j, policy->cpus) { > struct sugov_cpu *j_sg_cpu = &per_cpu(sugov_cpu, j); > - unsigned long j_util, j_max; > > sugov_get_util(j_sg_cpu); > sugov_iowait_apply(j_sg_cpu, time); > - j_util = j_sg_cpu->util; > - j_max = j_sg_cpu->max; > > - if (j_util * max > j_max * util) { > - util = j_util; > - max = j_max; > - } With the code removed above, max is only used in 2 places: - sugov_iowait_apply - map_util_freq I wonder if it would be better to just call arch_scale_cpu_capacity() in these 2 places instead of saving a copy in sg_policy and then reading it twice. arch_scaleu_cpu_capacity is already a per_cpu variable so accessing it should be pretty cheap. Thought ? > + util = max(j_sg_cpu->util, util); > } > > - return get_next_freq(sg_policy, util, max); > + return get_next_freq(sg_policy, util, sg_policy->max); > } > > static void > -- > 2.17.1 >
On 12/8/22 04:09, Viresh Kumar wrote: > On 07-12-22, 10:17, Lukasz Luba wrote: >> The max CPU capacity is the same for all CPUs sharing frequency domain >> and thus 'policy' object. There is a way to avoid heavy operations >> in a loop for each CPU by leveraging this knowledge. Thus, simplify >> the looping code in the sugov_next_freq_shared() and drop heavy >> multiplications. Instead, use simple max() to get the highest utilization >> from these CPUs. This is useful for platforms with many (4 or 6) little >> CPUs. >> >> The max CPU capacity must be fetched every time we are called, due to >> difficulties during the policy setup, where we are not able to get the >> normalized CPU capacity at the right time. >> >> The stored value in sugov_policy::max is also than used in >> sugov_iowait_apply() to calculate the right boost. Thus, that field is >> useful to have in that sugov_policy struct. >> >> Signed-off-by: Lukasz Luba <lukasz.luba@arm.com> >> --- >> kernel/sched/cpufreq_schedutil.c | 22 +++++++++++----------- >> 1 file changed, 11 insertions(+), 11 deletions(-) > > Looks okay to me. > > Acked-by: Viresh Kumar <viresh.kumar@linaro.org> > Thank you Viresh! As Rafael said, it will wait after 6.2-rc1 is out. Regards, Lukasz
On 12/8/22 08:37, Vincent Guittot wrote: > On Wed, 7 Dec 2022 at 11:17, Lukasz Luba <lukasz.luba@arm.com> wrote: >> >> The max CPU capacity is the same for all CPUs sharing frequency domain >> and thus 'policy' object. There is a way to avoid heavy operations >> in a loop for each CPU by leveraging this knowledge. Thus, simplify >> the looping code in the sugov_next_freq_shared() and drop heavy >> multiplications. Instead, use simple max() to get the highest utilization >> from these CPUs. This is useful for platforms with many (4 or 6) little >> CPUs. >> >> The max CPU capacity must be fetched every time we are called, due to >> difficulties during the policy setup, where we are not able to get the >> normalized CPU capacity at the right time. >> >> The stored value in sugov_policy::max is also than used in >> sugov_iowait_apply() to calculate the right boost. Thus, that field is >> useful to have in that sugov_policy struct. >> >> Signed-off-by: Lukasz Luba <lukasz.luba@arm.com> >> --- >> kernel/sched/cpufreq_schedutil.c | 22 +++++++++++----------- >> 1 file changed, 11 insertions(+), 11 deletions(-) >> >> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c >> index c19d6de67b7a..f9881f3d9488 100644 >> --- a/kernel/sched/cpufreq_schedutil.c >> +++ b/kernel/sched/cpufreq_schedutil.c >> @@ -158,10 +158,8 @@ static unsigned int get_next_freq(struct sugov_policy *sg_policy, >> >> static void sugov_get_util(struct sugov_cpu *sg_cpu) >> { >> - struct sugov_policy *sg_policy = sg_cpu->sg_policy; >> struct rq *rq = cpu_rq(sg_cpu->cpu); >> >> - sg_policy->max = arch_scale_cpu_capacity(sg_cpu->cpu); >> sg_cpu->bw_dl = cpu_bw_dl(rq); >> sg_cpu->util = effective_cpu_util(sg_cpu->cpu, cpu_util_cfs(sg_cpu->cpu), >> FREQUENCY_UTIL, NULL); >> @@ -317,6 +315,8 @@ static inline void ignore_dl_rate_limit(struct sugov_cpu *sg_cpu) >> static inline bool sugov_update_single_common(struct sugov_cpu *sg_cpu, >> u64 time, unsigned int flags) >> { >> + struct sugov_policy *sg_policy = sg_cpu->sg_policy; >> + >> sugov_iowait_boost(sg_cpu, time, flags); >> sg_cpu->last_update = time; >> >> @@ -325,6 +325,9 @@ static inline bool sugov_update_single_common(struct sugov_cpu *sg_cpu, >> if (!sugov_should_update_freq(sg_cpu->sg_policy, time)) >> return false; >> >> + /* Fetch the latest CPU capcity to avoid stale data */ >> + sg_policy->max = arch_scale_cpu_capacity(sg_cpu->cpu); >> + >> sugov_get_util(sg_cpu); >> sugov_iowait_apply(sg_cpu, time); >> >> @@ -414,25 +417,22 @@ static unsigned int sugov_next_freq_shared(struct sugov_cpu *sg_cpu, u64 time) >> { >> struct sugov_policy *sg_policy = sg_cpu->sg_policy; >> struct cpufreq_policy *policy = sg_policy->policy; >> - unsigned long util = 0, max = 1; >> + unsigned long util = 0; >> unsigned int j; >> >> + /* Fetch the latest CPU capcity to avoid stale data */ >> + sg_policy->max = arch_scale_cpu_capacity(sg_cpu->cpu); >> + >> for_each_cpu(j, policy->cpus) { >> struct sugov_cpu *j_sg_cpu = &per_cpu(sugov_cpu, j); >> - unsigned long j_util, j_max; >> >> sugov_get_util(j_sg_cpu); >> sugov_iowait_apply(j_sg_cpu, time); >> - j_util = j_sg_cpu->util; >> - j_max = j_sg_cpu->max; >> >> - if (j_util * max > j_max * util) { >> - util = j_util; >> - max = j_max; >> - } > > With the code removed above, max is only used in 2 places: > - sugov_iowait_apply > - map_util_freq > > I wonder if it would be better to just call arch_scale_cpu_capacity() > in these 2 places instead of saving a copy in sg_policy and then > reading it twice. The sugov_iowait_apply() is called in that loop, so probably I will add a new argument to that call and just feed it with the capacity value from one CPU, which was read before the loop. So, similarly what is in this patch. Otherwise, all of those per-cpu capacity vars would be accessed inside the sugov_iowait_apply() with sg_cpu->cpu. > > arch_scaleu_cpu_capacity is already a per_cpu variable so accessing it > should be pretty cheap. Yes and no, as you said this is per-cpu variable and would access them from one CPU, which is running that loop. They will have different pages and addresses so cache lines on that CPU. to avoiding trashing a cache lines on this running CPU let's read that capacity once, before the loop. Let's use the new arg to pass that value via one of the registers. In such, only one cache line would have to fetch that data into. So I thought this simple sg_policy->max would do the trick w/o a lot of hassle. > > Thought ? > I can change that and drop the sg_policy->max and call differently those capacity values. I will have to unfortunately drop Viresh's ACKs, since this will be a way different code. Thanks Vincent for the suggestion. Do you want me to go further with such approach and send a v3?
On Thu, 8 Dec 2022 at 11:06, Lukasz Luba <lukasz.luba@arm.com> wrote: > > > > On 12/8/22 08:37, Vincent Guittot wrote: > > On Wed, 7 Dec 2022 at 11:17, Lukasz Luba <lukasz.luba@arm.com> wrote: > >> > >> The max CPU capacity is the same for all CPUs sharing frequency domain > >> and thus 'policy' object. There is a way to avoid heavy operations > >> in a loop for each CPU by leveraging this knowledge. Thus, simplify > >> the looping code in the sugov_next_freq_shared() and drop heavy > >> multiplications. Instead, use simple max() to get the highest utilization > >> from these CPUs. This is useful for platforms with many (4 or 6) little > >> CPUs. > >> > >> The max CPU capacity must be fetched every time we are called, due to > >> difficulties during the policy setup, where we are not able to get the > >> normalized CPU capacity at the right time. > >> > >> The stored value in sugov_policy::max is also than used in > >> sugov_iowait_apply() to calculate the right boost. Thus, that field is > >> useful to have in that sugov_policy struct. > >> > >> Signed-off-by: Lukasz Luba <lukasz.luba@arm.com> > >> --- > >> kernel/sched/cpufreq_schedutil.c | 22 +++++++++++----------- > >> 1 file changed, 11 insertions(+), 11 deletions(-) > >> > >> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c > >> index c19d6de67b7a..f9881f3d9488 100644 > >> --- a/kernel/sched/cpufreq_schedutil.c > >> +++ b/kernel/sched/cpufreq_schedutil.c > >> @@ -158,10 +158,8 @@ static unsigned int get_next_freq(struct sugov_policy *sg_policy, > >> > >> static void sugov_get_util(struct sugov_cpu *sg_cpu) > >> { > >> - struct sugov_policy *sg_policy = sg_cpu->sg_policy; > >> struct rq *rq = cpu_rq(sg_cpu->cpu); > >> > >> - sg_policy->max = arch_scale_cpu_capacity(sg_cpu->cpu); > >> sg_cpu->bw_dl = cpu_bw_dl(rq); > >> sg_cpu->util = effective_cpu_util(sg_cpu->cpu, cpu_util_cfs(sg_cpu->cpu), > >> FREQUENCY_UTIL, NULL); > >> @@ -317,6 +315,8 @@ static inline void ignore_dl_rate_limit(struct sugov_cpu *sg_cpu) > >> static inline bool sugov_update_single_common(struct sugov_cpu *sg_cpu, > >> u64 time, unsigned int flags) > >> { > >> + struct sugov_policy *sg_policy = sg_cpu->sg_policy; > >> + > >> sugov_iowait_boost(sg_cpu, time, flags); > >> sg_cpu->last_update = time; > >> > >> @@ -325,6 +325,9 @@ static inline bool sugov_update_single_common(struct sugov_cpu *sg_cpu, > >> if (!sugov_should_update_freq(sg_cpu->sg_policy, time)) > >> return false; > >> > >> + /* Fetch the latest CPU capcity to avoid stale data */ > >> + sg_policy->max = arch_scale_cpu_capacity(sg_cpu->cpu); > >> + > >> sugov_get_util(sg_cpu); > >> sugov_iowait_apply(sg_cpu, time); > >> > >> @@ -414,25 +417,22 @@ static unsigned int sugov_next_freq_shared(struct sugov_cpu *sg_cpu, u64 time) > >> { > >> struct sugov_policy *sg_policy = sg_cpu->sg_policy; > >> struct cpufreq_policy *policy = sg_policy->policy; > >> - unsigned long util = 0, max = 1; > >> + unsigned long util = 0; > >> unsigned int j; > >> > >> + /* Fetch the latest CPU capcity to avoid stale data */ > >> + sg_policy->max = arch_scale_cpu_capacity(sg_cpu->cpu); > >> + > >> for_each_cpu(j, policy->cpus) { > >> struct sugov_cpu *j_sg_cpu = &per_cpu(sugov_cpu, j); > >> - unsigned long j_util, j_max; > >> > >> sugov_get_util(j_sg_cpu); > >> sugov_iowait_apply(j_sg_cpu, time); > >> - j_util = j_sg_cpu->util; > >> - j_max = j_sg_cpu->max; > >> > >> - if (j_util * max > j_max * util) { > >> - util = j_util; > >> - max = j_max; > >> - } > > > > With the code removed above, max is only used in 2 places: > > - sugov_iowait_apply > > - map_util_freq > > > > I wonder if it would be better to just call arch_scale_cpu_capacity() > > in these 2 places instead of saving a copy in sg_policy and then > > reading it twice. > > The sugov_iowait_apply() is called in that loop, so probably I will > add a new argument to that call and just feed it with the capacity value > from one CPU, which was read before the loop. So, similarly what is in > this patch. Otherwise, all of those per-cpu capacity vars would be > accessed inside the sugov_iowait_apply() with sg_cpu->cpu. Yes make sense > > > > > arch_scaleu_cpu_capacity is already a per_cpu variable so accessing it > > should be pretty cheap. > > Yes and no, as you said this is per-cpu variable and would access them > from one CPU, which is running that loop. They will have different pages > and addresses so cache lines on that CPU. to avoiding trashing a cache > lines on this running CPU let's read that capacity once, before the > loop. Let's use the new arg to pass that value via one of the > registers. In such, only one cache line would have to fetch that data > into. > > So I thought this simple sg_policy->max would do the trick w/o a lot > of hassle. For the shared mode, everything is located in sugov_next_freq_shared so you don't need to save the max value with your proposal above to change sugov_iowait_apply interface. This should be doable as well for single mode > > > > Thought ? > > > > I can change that and drop the sg_policy->max and call differently > those capacity values. I will have to unfortunately drop Viresh's ACKs, > since this will be a way different code. > > Thanks Vincent for the suggestion. Do you want me to go further with > such approach and send a v3? Don't know what Rafael and Viresh think but it seems that we don't need to save the return of arch_scale_cpu_capacity in ->max field but directly use it
On 12/8/22 10:31, Vincent Guittot wrote: > On Thu, 8 Dec 2022 at 11:06, Lukasz Luba <lukasz.luba@arm.com> wrote: >> >> >> >> On 12/8/22 08:37, Vincent Guittot wrote: >>> On Wed, 7 Dec 2022 at 11:17, Lukasz Luba <lukasz.luba@arm.com> wrote: >>>> >>>> The max CPU capacity is the same for all CPUs sharing frequency domain >>>> and thus 'policy' object. There is a way to avoid heavy operations >>>> in a loop for each CPU by leveraging this knowledge. Thus, simplify >>>> the looping code in the sugov_next_freq_shared() and drop heavy >>>> multiplications. Instead, use simple max() to get the highest utilization >>>> from these CPUs. This is useful for platforms with many (4 or 6) little >>>> CPUs. >>>> >>>> The max CPU capacity must be fetched every time we are called, due to >>>> difficulties during the policy setup, where we are not able to get the >>>> normalized CPU capacity at the right time. >>>> >>>> The stored value in sugov_policy::max is also than used in >>>> sugov_iowait_apply() to calculate the right boost. Thus, that field is >>>> useful to have in that sugov_policy struct. >>>> >>>> Signed-off-by: Lukasz Luba <lukasz.luba@arm.com> >>>> --- >>>> kernel/sched/cpufreq_schedutil.c | 22 +++++++++++----------- >>>> 1 file changed, 11 insertions(+), 11 deletions(-) >>>> >>>> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c >>>> index c19d6de67b7a..f9881f3d9488 100644 >>>> --- a/kernel/sched/cpufreq_schedutil.c >>>> +++ b/kernel/sched/cpufreq_schedutil.c >>>> @@ -158,10 +158,8 @@ static unsigned int get_next_freq(struct sugov_policy *sg_policy, >>>> >>>> static void sugov_get_util(struct sugov_cpu *sg_cpu) >>>> { >>>> - struct sugov_policy *sg_policy = sg_cpu->sg_policy; >>>> struct rq *rq = cpu_rq(sg_cpu->cpu); >>>> >>>> - sg_policy->max = arch_scale_cpu_capacity(sg_cpu->cpu); >>>> sg_cpu->bw_dl = cpu_bw_dl(rq); >>>> sg_cpu->util = effective_cpu_util(sg_cpu->cpu, cpu_util_cfs(sg_cpu->cpu), >>>> FREQUENCY_UTIL, NULL); >>>> @@ -317,6 +315,8 @@ static inline void ignore_dl_rate_limit(struct sugov_cpu *sg_cpu) >>>> static inline bool sugov_update_single_common(struct sugov_cpu *sg_cpu, >>>> u64 time, unsigned int flags) >>>> { >>>> + struct sugov_policy *sg_policy = sg_cpu->sg_policy; >>>> + >>>> sugov_iowait_boost(sg_cpu, time, flags); >>>> sg_cpu->last_update = time; >>>> >>>> @@ -325,6 +325,9 @@ static inline bool sugov_update_single_common(struct sugov_cpu *sg_cpu, >>>> if (!sugov_should_update_freq(sg_cpu->sg_policy, time)) >>>> return false; >>>> >>>> + /* Fetch the latest CPU capcity to avoid stale data */ >>>> + sg_policy->max = arch_scale_cpu_capacity(sg_cpu->cpu); >>>> + >>>> sugov_get_util(sg_cpu); >>>> sugov_iowait_apply(sg_cpu, time); >>>> >>>> @@ -414,25 +417,22 @@ static unsigned int sugov_next_freq_shared(struct sugov_cpu *sg_cpu, u64 time) >>>> { >>>> struct sugov_policy *sg_policy = sg_cpu->sg_policy; >>>> struct cpufreq_policy *policy = sg_policy->policy; >>>> - unsigned long util = 0, max = 1; >>>> + unsigned long util = 0; >>>> unsigned int j; >>>> >>>> + /* Fetch the latest CPU capcity to avoid stale data */ >>>> + sg_policy->max = arch_scale_cpu_capacity(sg_cpu->cpu); >>>> + >>>> for_each_cpu(j, policy->cpus) { >>>> struct sugov_cpu *j_sg_cpu = &per_cpu(sugov_cpu, j); >>>> - unsigned long j_util, j_max; >>>> >>>> sugov_get_util(j_sg_cpu); >>>> sugov_iowait_apply(j_sg_cpu, time); >>>> - j_util = j_sg_cpu->util; >>>> - j_max = j_sg_cpu->max; >>>> >>>> - if (j_util * max > j_max * util) { >>>> - util = j_util; >>>> - max = j_max; >>>> - } >>> >>> With the code removed above, max is only used in 2 places: >>> - sugov_iowait_apply >>> - map_util_freq >>> >>> I wonder if it would be better to just call arch_scale_cpu_capacity() >>> in these 2 places instead of saving a copy in sg_policy and then >>> reading it twice. >> >> The sugov_iowait_apply() is called in that loop, so probably I will >> add a new argument to that call and just feed it with the capacity value >> from one CPU, which was read before the loop. So, similarly what is in >> this patch. Otherwise, all of those per-cpu capacity vars would be >> accessed inside the sugov_iowait_apply() with sg_cpu->cpu. > > Yes make sense > >> >>> >>> arch_scaleu_cpu_capacity is already a per_cpu variable so accessing it >>> should be pretty cheap. >> >> Yes and no, as you said this is per-cpu variable and would access them >> from one CPU, which is running that loop. They will have different pages >> and addresses so cache lines on that CPU. to avoiding trashing a cache >> lines on this running CPU let's read that capacity once, before the >> loop. Let's use the new arg to pass that value via one of the >> registers. In such, only one cache line would have to fetch that data >> into. >> >> So I thought this simple sg_policy->max would do the trick w/o a lot >> of hassle. > > For the shared mode, everything is located in sugov_next_freq_shared > so you don't need to save the max value with your proposal above to > change sugov_iowait_apply interface. > > This should be doable as well for single mode > >>> >>> Thought ? >>> >> >> I can change that and drop the sg_policy->max and call differently >> those capacity values. I will have to unfortunately drop Viresh's ACKs, >> since this will be a way different code. >> >> Thanks Vincent for the suggestion. Do you want me to go further with >> such approach and send a v3? > > Don't know what Rafael and Viresh think but it seems that we don't > need to save the return of arch_scale_cpu_capacity in ->max field but > directly use it Yes I agree, we don't need to, but I will have to modify a few function calls and args. So IMO we have agreed. I won't call the call arch_scale_cpu_capacity() in these 2 places, but I will make it with the local var and data fetched as little as possible.
On Thu, 8 Dec 2022 at 11:56, Lukasz Luba <lukasz.luba@arm.com> wrote: > > > > On 12/8/22 10:31, Vincent Guittot wrote: > > On Thu, 8 Dec 2022 at 11:06, Lukasz Luba <lukasz.luba@arm.com> wrote: > >> > >> > >> > >> On 12/8/22 08:37, Vincent Guittot wrote: > >>> On Wed, 7 Dec 2022 at 11:17, Lukasz Luba <lukasz.luba@arm.com> wrote: > >>>> > >>>> The max CPU capacity is the same for all CPUs sharing frequency domain > >>>> and thus 'policy' object. There is a way to avoid heavy operations > >>>> in a loop for each CPU by leveraging this knowledge. Thus, simplify > >>>> the looping code in the sugov_next_freq_shared() and drop heavy > >>>> multiplications. Instead, use simple max() to get the highest utilization > >>>> from these CPUs. This is useful for platforms with many (4 or 6) little > >>>> CPUs. > >>>> > >>>> The max CPU capacity must be fetched every time we are called, due to > >>>> difficulties during the policy setup, where we are not able to get the > >>>> normalized CPU capacity at the right time. > >>>> > >>>> The stored value in sugov_policy::max is also than used in > >>>> sugov_iowait_apply() to calculate the right boost. Thus, that field is > >>>> useful to have in that sugov_policy struct. > >>>> > >>>> Signed-off-by: Lukasz Luba <lukasz.luba@arm.com> > >>>> --- > >>>> kernel/sched/cpufreq_schedutil.c | 22 +++++++++++----------- > >>>> 1 file changed, 11 insertions(+), 11 deletions(-) > >>>> > >>>> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c > >>>> index c19d6de67b7a..f9881f3d9488 100644 > >>>> --- a/kernel/sched/cpufreq_schedutil.c > >>>> +++ b/kernel/sched/cpufreq_schedutil.c > >>>> @@ -158,10 +158,8 @@ static unsigned int get_next_freq(struct sugov_policy *sg_policy, > >>>> > >>>> static void sugov_get_util(struct sugov_cpu *sg_cpu) > >>>> { > >>>> - struct sugov_policy *sg_policy = sg_cpu->sg_policy; > >>>> struct rq *rq = cpu_rq(sg_cpu->cpu); > >>>> > >>>> - sg_policy->max = arch_scale_cpu_capacity(sg_cpu->cpu); > >>>> sg_cpu->bw_dl = cpu_bw_dl(rq); > >>>> sg_cpu->util = effective_cpu_util(sg_cpu->cpu, cpu_util_cfs(sg_cpu->cpu), > >>>> FREQUENCY_UTIL, NULL); > >>>> @@ -317,6 +315,8 @@ static inline void ignore_dl_rate_limit(struct sugov_cpu *sg_cpu) > >>>> static inline bool sugov_update_single_common(struct sugov_cpu *sg_cpu, > >>>> u64 time, unsigned int flags) > >>>> { > >>>> + struct sugov_policy *sg_policy = sg_cpu->sg_policy; > >>>> + > >>>> sugov_iowait_boost(sg_cpu, time, flags); > >>>> sg_cpu->last_update = time; > >>>> > >>>> @@ -325,6 +325,9 @@ static inline bool sugov_update_single_common(struct sugov_cpu *sg_cpu, > >>>> if (!sugov_should_update_freq(sg_cpu->sg_policy, time)) > >>>> return false; > >>>> > >>>> + /* Fetch the latest CPU capcity to avoid stale data */ > >>>> + sg_policy->max = arch_scale_cpu_capacity(sg_cpu->cpu); > >>>> + > >>>> sugov_get_util(sg_cpu); > >>>> sugov_iowait_apply(sg_cpu, time); > >>>> > >>>> @@ -414,25 +417,22 @@ static unsigned int sugov_next_freq_shared(struct sugov_cpu *sg_cpu, u64 time) > >>>> { > >>>> struct sugov_policy *sg_policy = sg_cpu->sg_policy; > >>>> struct cpufreq_policy *policy = sg_policy->policy; > >>>> - unsigned long util = 0, max = 1; > >>>> + unsigned long util = 0; > >>>> unsigned int j; > >>>> > >>>> + /* Fetch the latest CPU capcity to avoid stale data */ > >>>> + sg_policy->max = arch_scale_cpu_capacity(sg_cpu->cpu); > >>>> + > >>>> for_each_cpu(j, policy->cpus) { > >>>> struct sugov_cpu *j_sg_cpu = &per_cpu(sugov_cpu, j); > >>>> - unsigned long j_util, j_max; > >>>> > >>>> sugov_get_util(j_sg_cpu); > >>>> sugov_iowait_apply(j_sg_cpu, time); > >>>> - j_util = j_sg_cpu->util; > >>>> - j_max = j_sg_cpu->max; > >>>> > >>>> - if (j_util * max > j_max * util) { > >>>> - util = j_util; > >>>> - max = j_max; > >>>> - } > >>> > >>> With the code removed above, max is only used in 2 places: > >>> - sugov_iowait_apply > >>> - map_util_freq > >>> > >>> I wonder if it would be better to just call arch_scale_cpu_capacity() > >>> in these 2 places instead of saving a copy in sg_policy and then > >>> reading it twice. > >> > >> The sugov_iowait_apply() is called in that loop, so probably I will > >> add a new argument to that call and just feed it with the capacity value > >> from one CPU, which was read before the loop. So, similarly what is in > >> this patch. Otherwise, all of those per-cpu capacity vars would be > >> accessed inside the sugov_iowait_apply() with sg_cpu->cpu. > > > > Yes make sense > > > >> > >>> > >>> arch_scaleu_cpu_capacity is already a per_cpu variable so accessing it > >>> should be pretty cheap. > >> > >> Yes and no, as you said this is per-cpu variable and would access them > >> from one CPU, which is running that loop. They will have different pages > >> and addresses so cache lines on that CPU. to avoiding trashing a cache > >> lines on this running CPU let's read that capacity once, before the > >> loop. Let's use the new arg to pass that value via one of the > >> registers. In such, only one cache line would have to fetch that data > >> into. > >> > >> So I thought this simple sg_policy->max would do the trick w/o a lot > >> of hassle. > > > > For the shared mode, everything is located in sugov_next_freq_shared > > so you don't need to save the max value with your proposal above to > > change sugov_iowait_apply interface. > > > > This should be doable as well for single mode > > > >>> > >>> Thought ? > >>> > >> > >> I can change that and drop the sg_policy->max and call differently > >> those capacity values. I will have to unfortunately drop Viresh's ACKs, > >> since this will be a way different code. > >> > >> Thanks Vincent for the suggestion. Do you want me to go further with > >> such approach and send a v3? > > > > Don't know what Rafael and Viresh think but it seems that we don't > > need to save the return of arch_scale_cpu_capacity in ->max field but > > directly use it > > Yes I agree, we don't need to, but I will have to modify a few function > calls and args. > > So IMO we have agreed. I won't call the call arch_scale_cpu_capacity() > in these 2 places, but I will make it with the local var and data > fetched as little as possible. yes
Hi all, This v2 is an attempt to optimize some not needed operations in the frequency change code path for the shared freq. domain. There was different approach which was too aggressive and failed do to working on a state CPU capacity information. changes: v2: - split the patch into two (Viresh) v1: - simple approach which fetches CPU capacity every time it's needed, not relaying on the setup value, which was causing issues. Regards, Lukasz Lukasz Luba (2): cpufreq: schedutil: Introduce single max CPU capacity for freqency domain cpufreq: schedutil: Optimize operations with single max CPU capacity kernel/sched/cpufreq_schedutil.c | 35 +++++++++++++++++++------------- 1 file changed, 21 insertions(+), 14 deletions(-)