Messages in this thread | | | From | Vincent Guittot <> | Date | Fri, 15 Jun 2018 14:18:07 +0200 | Subject | Re: [PATCH v6 03/11] sched/rt: add rt_rq utilization tracking |
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Hi Dietmar,
On 15 June 2018 at 13:52, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote: > On 06/08/2018 02:09 PM, Vincent Guittot wrote: >> schedutil governor relies on cfs_rq's util_avg to choose the OPP when cfs >> tasks are running. When the CPU is overloaded by cfs and rt tasks, cfs tasks >> are preempted by rt tasks and in this case util_avg reflects the remaining >> capacity but not what cfs want to use. In such case, schedutil can select a >> lower OPP whereas the CPU is overloaded. In order to have a more accurate >> view of the utilization of the CPU, we track the utilization of rt tasks. >> >> rt_rq uses rq_clock_task and cfs_rq uses cfs_rq_clock_task but they are >> the same at the root group level, so the PELT windows of the util_sum are >> aligned. >> >> Cc: Ingo Molnar <mingo@redhat.com> >> Cc: Peter Zijlstra <peterz@infradead.org> >> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> > > [...] > > ; >> diff --git a/kernel/sched/pelt.c b/kernel/sched/pelt.c >> index 4174582..81c0d7e 100644 >> --- a/kernel/sched/pelt.c >> +++ b/kernel/sched/pelt.c >> @@ -307,3 +307,25 @@ int __update_load_avg_cfs_rq(u64 now, int cpu, struct cfs_rq *cfs_rq) >> >> return 0; >> } >> + >> +/* >> + * rt_rq: >> + * >> + * util_sum = \Sum se->avg.util_sum but se->avg.util_sum is not tracked >> + * util_sum = cpu_scale * load_sum >> + * runnable_load_sum = load_sum >> + * >> + */ >> + >> +int update_rt_rq_load_avg(u64 now, struct rq *rq, int running) >> +{ >> + if (___update_load_sum(now, rq->cpu, &rq->avg_rt, >> + running, >> + running, >> + running)) { > > The patch clearly says that this is about utilization but what happens > to load and runnable load for the rt rq part when you call > ___update_load_sum() with load=[0,1] and runnable=[0,1]?
I would say the same than what happens for se which has ___update_load_sum(now, cpu, &se->avg, !!se->on_rq, !!se->on_rq, cfs_rq->curr == se))
> > It looks like that the math would require 1024 instead of 1 for load and > runnable so that we would see a load_avg or runnable_load_avg != 0.
why does it require 1024 ? the min weight of a task is 15 and the min share of a sched group is 2. AFAICT, there is no requirement mainly because we are not using them as they will not give any additional information compare to util_avg
> > 1594.075128: bprint: update_rt_rq_load_avg: now=1593937228087 cpu=4 running=1 > 1594.075129: bprint: update_rt_rq_load_avg: delta=3068 cpu=4 load=1 runnable=1 running=1 scale_freq=1024 scale_cpu=1024 periods=2 > 1594.075130: bprint: update_rt_rq_load_avg: load_sum=23927 +2879 runnable_load_sum=23927 +2879 util_sum=24506165 +2948096 > 1594.075130: bprint: update_rt_rq_load_avg: load_avg=0 runnable_load_avg=0 util_avg=513 > > IMHO, the patch should say whether load and runnable load are supported as well or not.
Although it is stated that we track only utilization , i can probably mentioned clearly that load_avg and runnable_load_avg are useless
Vincent > > [...]
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