Messages in this thread Patch in this message | | | From | douglas.raillard@arm ... | Subject | [RFC PATCH 7/7] sched/cpufreq: Boost schedutil frequency ramp up | Date | Wed, 8 May 2019 18:43:01 +0100 |
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From: Douglas RAILLARD <douglas.raillard@arm.com>
In some situations, it can be interesting to spend temporarily more power if that can give a useful frequency boost.
The sugov_cpu_is_busy() heuristic is reused to check if there has been some idle time on all CPUs in the considered perf domain since last call to schedutil's get_next_freq(). If not, it is assumed that at least one CPU is in a frequency ramp up phase and the domain will be allowed to spend extra power to reach a stable OPP in a shorter amount of time.
Since the extra power expenditure is bounded, it cannot skyrocket even on platforms with a large number of cores in the same frequency domain and/or very high ratio between lowest and highest OPP cost.
Signed-off-by: Douglas RAILLARD <douglas.raillard@arm.com> --- kernel/sched/cpufreq_schedutil.c | 22 +++++++++++++++++----- 1 file changed, 17 insertions(+), 5 deletions(-)
diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c index ce4b90cafbb5..513b32bf14c5 100644 --- a/kernel/sched/cpufreq_schedutil.c +++ b/kernel/sched/cpufreq_schedutil.c @@ -218,6 +218,8 @@ static void sugov_cpu_is_busy_update(struct sugov_cpu *sg_cpu * @sg_policy: schedutil policy object to compute the new frequency for. * @util: Current CPU utilization. * @max: CPU capacity. + * @busy: true if at least one CPU in the policy is busy, which means it had no + * idle time since its last frequency change. * * If the utilization is frequency-invariant, choose the new frequency to be * proportional to it, that is @@ -231,20 +233,28 @@ static void sugov_cpu_is_busy_update(struct sugov_cpu *sg_cpu * * Take C = 1.25 for the frequency tipping point at (util / max) = 0.8. * + * An energy-aware boost is then applied if busy is true. The boost will allow + * selecting frequencies at most twice as costly in term of energy. + * * The lowest driver-supported frequency which is equal or greater than the raw * next_freq (as calculated above) is returned, subject to policy min/max and * cpufreq driver limitations. */ static unsigned int get_next_freq(struct sugov_policy *sg_policy, - unsigned long util, unsigned long max) + unsigned long util, unsigned long max, + bool busy) { struct cpufreq_policy *policy = sg_policy->policy; unsigned int freq = arch_scale_freq_invariant() ? policy->cpuinfo.max_freq : policy->cur; struct em_perf_domain *pd = sugov_policy_get_pd(sg_policy); - /* Maximum power we are ready to spend. */ - unsigned int cost_margin = 0; + /* + * Maximum power we are ready to spend. + * When one CPU is busy in the policy, we apply a boost to help it reach + * the needed frequency faster. + */ + unsigned int cost_margin = busy ? 1024/2 : 0; freq = map_util_freq(util, freq, max); @@ -534,7 +544,7 @@ static void sugov_update_single(struct update_util_data *hook, u64 time, sugov_cpu_is_busy_update(sg_cpu, util); max = sg_cpu->max; util = sugov_iowait_apply(sg_cpu, time, util, max); - next_f = get_next_freq(sg_policy, util, max); + next_f = get_next_freq(sg_policy, util, max, busy); /* * Do not reduce the frequency if the CPU has not been idle * recently, as the reduction is likely to be premature then. @@ -567,6 +577,7 @@ static unsigned int sugov_next_freq_shared(struct sugov_cpu *sg_cpu, u64 time) unsigned long util = 0, max = 1; unsigned int j; unsigned long sg_cpu_util = 0; + bool busy = false; for_each_cpu(j, policy->cpus) { struct sugov_cpu *j_sg_cpu = &per_cpu(sugov_cpu, j); @@ -577,6 +588,7 @@ static unsigned int sugov_next_freq_shared(struct sugov_cpu *sg_cpu, u64 time) sg_cpu_util = j_util; j_max = j_sg_cpu->max; j_util = sugov_iowait_apply(j_sg_cpu, time, j_util, j_max); + busy |= sugov_cpu_is_busy(j_sg_cpu); if (j_util * max > j_max * util) { util = j_util; @@ -592,7 +604,7 @@ static unsigned int sugov_next_freq_shared(struct sugov_cpu *sg_cpu, u64 time) */ sugov_cpu_is_busy_update(sg_cpu, sg_cpu_util); - return get_next_freq(sg_policy, util, max); + return get_next_freq(sg_policy, util, max, busy); } static void -- 2.21.0
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