| Message ID | 20230827233203.1315953-5-qyousef@layalina.io (mailing list archive) |
|---|---|
| State | RFC, archived |
| Headers | show |
| Series | sched: cpufreq: Remove magic margins | expand |
On Mon, Aug 28, 2023 at 12:32:00AM +0100, Qais Yousef wrote: > Instead of the magical 1.25 headroom, use the new approximate_util_avg() > to provide headroom based on the dvfs_update_delay; which is the period > at which the cpufreq governor will send DVFS updates to the hardware. > > Add a new percpu dvfs_update_delay that can be cheaply accessed whenever > apply_dvfs_headroom() is called. We expect cpufreq governors that rely > on util to drive its DVFS logic/algorithm to populate these percpu > variables. schedutil is the only such governor at the moment. > > Signed-off-by: Qais Yousef (Google) <qyousef@layalina.io> > --- > kernel/sched/core.c | 3 ++- > kernel/sched/cpufreq_schedutil.c | 10 +++++++++- > kernel/sched/sched.h | 25 ++++++++++++++----------- > 3 files changed, 25 insertions(+), 13 deletions(-) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 602e369753a3..f56eb44745a8 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -116,6 +116,7 @@ EXPORT_TRACEPOINT_SYMBOL_GPL(sched_util_est_se_tp); > EXPORT_TRACEPOINT_SYMBOL_GPL(sched_update_nr_running_tp); > > DEFINE_PER_CPU_SHARED_ALIGNED(struct rq, runqueues); > +DEFINE_PER_CPU_SHARED_ALIGNED(u64, dvfs_update_delay); This makes no sense, why are you using SHARED_ALIGNED and thus wasting an entire cacheline for the one variable?
On 09/07/23 13:34, Peter Zijlstra wrote: > On Mon, Aug 28, 2023 at 12:32:00AM +0100, Qais Yousef wrote: > > Instead of the magical 1.25 headroom, use the new approximate_util_avg() > > to provide headroom based on the dvfs_update_delay; which is the period > > at which the cpufreq governor will send DVFS updates to the hardware. > > > > Add a new percpu dvfs_update_delay that can be cheaply accessed whenever > > apply_dvfs_headroom() is called. We expect cpufreq governors that rely > > on util to drive its DVFS logic/algorithm to populate these percpu > > variables. schedutil is the only such governor at the moment. > > > > Signed-off-by: Qais Yousef (Google) <qyousef@layalina.io> > > --- > > kernel/sched/core.c | 3 ++- > > kernel/sched/cpufreq_schedutil.c | 10 +++++++++- > > kernel/sched/sched.h | 25 ++++++++++++++----------- > > 3 files changed, 25 insertions(+), 13 deletions(-) > > > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > > index 602e369753a3..f56eb44745a8 100644 > > --- a/kernel/sched/core.c > > +++ b/kernel/sched/core.c > > @@ -116,6 +116,7 @@ EXPORT_TRACEPOINT_SYMBOL_GPL(sched_util_est_se_tp); > > EXPORT_TRACEPOINT_SYMBOL_GPL(sched_update_nr_running_tp); > > > > DEFINE_PER_CPU_SHARED_ALIGNED(struct rq, runqueues); > > +DEFINE_PER_CPU_SHARED_ALIGNED(u64, dvfs_update_delay); > > This makes no sense, why are you using SHARED_ALIGNED and thus wasting > an entire cacheline for the one variable? Err, brain fart. Sorry. Thanks -- Qais Yousef
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 602e369753a3..f56eb44745a8 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -116,6 +116,7 @@ EXPORT_TRACEPOINT_SYMBOL_GPL(sched_util_est_se_tp); EXPORT_TRACEPOINT_SYMBOL_GPL(sched_update_nr_running_tp); DEFINE_PER_CPU_SHARED_ALIGNED(struct rq, runqueues); +DEFINE_PER_CPU_SHARED_ALIGNED(u64, dvfs_update_delay); #ifdef CONFIG_SCHED_DEBUG /* @@ -7439,7 +7440,7 @@ unsigned long effective_cpu_util(int cpu, unsigned long util_cfs, * frequency will be gracefully reduced with the utilization decay. */ if (type == FREQUENCY_UTIL) { - util = apply_dvfs_headroom(util_cfs) + cpu_util_rt(rq); + util = apply_dvfs_headroom(util_cfs, cpu) + cpu_util_rt(rq); util = uclamp_rq_util_with(rq, util, p); } else { util = util_cfs + cpu_util_rt(rq); diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c index 0c7565ac31fb..04aa06846f31 100644 --- a/kernel/sched/cpufreq_schedutil.c +++ b/kernel/sched/cpufreq_schedutil.c @@ -519,15 +519,21 @@ rate_limit_us_store(struct gov_attr_set *attr_set, const char *buf, size_t count struct sugov_tunables *tunables = to_sugov_tunables(attr_set); struct sugov_policy *sg_policy; unsigned int rate_limit_us; + int cpu; if (kstrtouint(buf, 10, &rate_limit_us)) return -EINVAL; tunables->rate_limit_us = rate_limit_us; - list_for_each_entry(sg_policy, &attr_set->policy_list, tunables_hook) + list_for_each_entry(sg_policy, &attr_set->policy_list, tunables_hook) { + sg_policy->freq_update_delay_ns = rate_limit_us * NSEC_PER_USEC; + for_each_cpu(cpu, sg_policy->policy->cpus) + per_cpu(dvfs_update_delay, cpu) = rate_limit_us; + } + return count; } @@ -772,6 +778,8 @@ static int sugov_start(struct cpufreq_policy *policy) memset(sg_cpu, 0, sizeof(*sg_cpu)); sg_cpu->cpu = cpu; sg_cpu->sg_policy = sg_policy; + + per_cpu(dvfs_update_delay, cpu) = sg_policy->tunables->rate_limit_us; } if (policy_is_shared(policy)) diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 2b889ad399de..e06e512af192 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -3001,6 +3001,15 @@ unsigned long effective_cpu_util(int cpu, unsigned long util_cfs, unsigned long approximate_util_avg(unsigned long util, u64 delta); u64 approximate_runtime(unsigned long util); +/* + * Any governor that relies on util signal to drive DVFS, must populate these + * percpu dvfs_update_delay variables. + * + * It should describe the rate/delay at which the governor sends DVFS freq + * update to the hardware in us. + */ +DECLARE_PER_CPU_SHARED_ALIGNED(u64, dvfs_update_delay); + /* * DVFS decision are made at discrete points. If CPU stays busy, the util will * continue to grow, which means it could need to run at a higher frequency @@ -3010,20 +3019,14 @@ u64 approximate_runtime(unsigned long util); * to run at adequate performance point. * * This function provides enough headroom to provide adequate performance - * assuming the CPU continues to be busy. - * - * At the moment it is a constant multiplication with 1.25. + * assuming the CPU continues to be busy. This headroom is based on the + * dvfs_update_delay of the cpufreq governor. * - * TODO: The headroom should be a function of the delay. 25% is too high - * especially on powerful systems. For example, if the delay is 500us, it makes - * more sense to give a small headroom as the next decision point is not far - * away and will follow the util if it continues to rise. On the other hand if - * the delay is 10ms, then we need a bigger headroom so the CPU won't struggle - * at a lower frequency if it never goes to idle until then. + * XXX: Should we provide headroom when the util is decaying? */ -static inline unsigned long apply_dvfs_headroom(unsigned long util) +static inline unsigned long apply_dvfs_headroom(unsigned long util, int cpu) { - return util + (util >> 2); + return approximate_util_avg(util, per_cpu(dvfs_update_delay, cpu)); } /*
Instead of the magical 1.25 headroom, use the new approximate_util_avg() to provide headroom based on the dvfs_update_delay; which is the period at which the cpufreq governor will send DVFS updates to the hardware. Add a new percpu dvfs_update_delay that can be cheaply accessed whenever apply_dvfs_headroom() is called. We expect cpufreq governors that rely on util to drive its DVFS logic/algorithm to populate these percpu variables. schedutil is the only such governor at the moment. Signed-off-by: Qais Yousef (Google) <qyousef@layalina.io> --- kernel/sched/core.c | 3 ++- kernel/sched/cpufreq_schedutil.c | 10 +++++++++- kernel/sched/sched.h | 25 ++++++++++++++----------- 3 files changed, 25 insertions(+), 13 deletions(-)