Re: [PATCH 2/2] sched: cpufreq: use rt_avg as estimate of required RT CPU capacity
From: Rafael J. Wysocki <hidden>
Date: 2016-08-31 01:25:20
Also in:
lkml
On Friday, August 26, 2016 11:40:48 AM Steve Muckle wrote:
A policy of going to fmax on any RT activity will be detrimental for power on many platforms. Often RT accounts for only a small amount of CPU activity so sending the CPU frequency to fmax is overkill. Worse still, some platforms may not be able to even complete the CPU frequency change before the RT activity has already completed. Cpufreq governors have not treated RT activity this way in the past so it is not part of the expected semantics of the RT scheduling class. The DL class offers guarantees about task completion and could be used for this purpose. Modify the schedutil algorithm to instead use rt_avg as an estimate of RT utilization of the CPU. Based on previous work by Vincent Guittot [off-list ref].
If we do it for RT, why not to do a similar thing for DL? As in the original patch from Peter, for example?
quoted hunk ↗ jump to hunk
Signed-off-by: Steve Muckle <redacted> --- kernel/sched/cpufreq_schedutil.c | 26 +++++++++++++++++--------- 1 file changed, 17 insertions(+), 9 deletions(-)diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c index cb8a77b1ef1b..89094a466250 100644 --- a/kernel/sched/cpufreq_schedutil.c +++ b/kernel/sched/cpufreq_schedutil.c@@ -146,13 +146,21 @@ static unsigned int get_next_freq(struct sugov_cpu *sg_cpu, unsigned long util, static void sugov_get_util(unsigned long *util, unsigned long *max) { - struct rq *rq = this_rq(); - unsigned long cfs_max; + int cpu = smp_processor_id(); + struct rq *rq = cpu_rq(cpu); + unsigned long max_cap, rt; + s64 delta; - cfs_max = arch_scale_cpu_capacity(NULL, smp_processor_id()); + max_cap = arch_scale_cpu_capacity(NULL, cpu); - *util = min(rq->cfs.avg.util_avg, cfs_max); - *max = cfs_max; + delta = rq_clock(rq) - rq->age_stamp; + if (unlikely(delta < 0)) + delta = 0; + rt = div64_u64(rq->rt_avg, sched_avg_period() + delta); + rt = (rt * max_cap) >> SCHED_CAPACITY_SHIFT;
These computations are rather heavy, so I wonder if they are avoidable based on the flags, for example? Plus is SCHED_CAPACITY_SHIFT actually defined for all architectures? One more ugly thing is about using rq_clock(rq) directly from here whereas we pass it around as the 'time' argument elsewhere.
+ + *util = min(rq->cfs.avg.util_avg + rt, max_cap); + *max = max_cap; }
Thanks, Rafael