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    SubjectRe: [Resend PATCH] psi : calc cfs task memstall time more precisely
    On Wed, Nov 3, 2021 at 3:47 AM Johannes Weiner <hannes@cmpxchg.org> wrote:
    >
    > CC peterz as well for rt and timekeeping magic
    >
    > On Fri, Oct 15, 2021 at 02:16:52PM +0800, Huangzhaoyang wrote:
    > > From: Zhaoyang Huang <zhaoyang.huang@unisoc.com>
    > >
    > > In an EAS enabled system, there are two scenarios discordant to current design,
    > >
    > > 1. workload used to be heavy uneven among cores for sake of scheduler policy.
    > > RT task usually preempts CFS task in little core.
    > > 2. CFS task's memstall time is counted as simple as exit - entry so far, which
    > > ignore the preempted time by RT, DL and Irqs.
    > >
    > > With these two constraints, the percpu nonidle time would be mainly consumed by
    > > none CFS tasks and couldn't be averaged. Eliminating them by calc the time growth
    > > via the proportion of cfs_rq's utilization on the whole rq.
    > >
    > > eg.
    > > Here is the scenario which this commit want to fix, that is the rt and irq consume
    > > some utilization of the whole rq. This scenario could be typical in a core
    > > which is assigned to deal with all irqs. Furthermore, the rt task used to run on
    > > little core under EAS.
    > >
    > > Binder:305_3-314 [002] d..1 257.880195: psi_memtime_fixup: original:30616,adjusted:25951,se:89,cfs:353,rt:139,dl:0,irq:18
    > > droid.phone-1525 [001] d..1 265.145492: psi_memtime_fixup: original:61616,adjusted:53492,se:55,cfs:225,rt:121,dl:0,irq:15
    > >
    > > Signed-off-by: Zhaoyang Huang <zhaoyang.huang@unisoc.com>
    > > ---
    > > kernel/sched/psi.c | 20 +++++++++++++++++++-
    > > 1 file changed, 19 insertions(+), 1 deletion(-)
    > >
    > > diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
    > > index cc25a3c..754a836 100644
    > > --- a/kernel/sched/psi.c
    > > +++ b/kernel/sched/psi.c
    > > @@ -182,6 +182,8 @@ struct psi_group psi_system = {
    > >
    > > static void psi_avgs_work(struct work_struct *work);
    > >
    > > +static unsigned long psi_memtime_fixup(u32 growth);
    > > +
    > > static void group_init(struct psi_group *group)
    > > {
    > > int cpu;
    > > @@ -492,6 +494,21 @@ static u64 window_update(struct psi_window *win, u64 now, u64 value)
    > > return growth;
    > > }
    > >
    > > +static unsigned long psi_memtime_fixup(u32 growth)
    > > +{
    > > + struct rq *rq = task_rq(current);
    > > + unsigned long growth_fixed = (unsigned long)growth;
    > > +
    > > + if (!(current->policy == SCHED_NORMAL || current->policy == SCHED_BATCH))
    > > + return growth_fixed;
    > > +
    > > + if (current->in_memstall)
    > > + growth_fixed = div64_ul((1024 - rq->avg_rt.util_avg - rq->avg_dl.util_avg
    > > + - rq->avg_irq.util_avg + 1) * growth, 1024);
    > > +
    > > + return growth_fixed;
    > > +}
    > > +
    > > static void init_triggers(struct psi_group *group, u64 now)
    > > {
    > > struct psi_trigger *t;
    > > @@ -658,6 +675,7 @@ static void record_times(struct psi_group_cpu *groupc, u64 now)
    > > }
    > >
    > > if (groupc->state_mask & (1 << PSI_MEM_SOME)) {
    > > + delta = psi_memtime_fixup(delta);
    >
    add vincent for advise on cpu load mechanism

    > Ok, so we want to deduct IRQ and RT preemption time from the memstall
    > period of an active reclaimer, since it's technically not stalled on
    > memory during this time but on CPU.
    >
    > However, we do NOT want to deduct IRQ and RT time from memstalls that
    > are sleeping on refaults swapins, since they are not affected by what
    > is going on on the CPU.
    >
    > Does util_avg capture that difference? I'm not confident it does - but
    > correct me if I'm wrong. We need length of time during which and IRQ
    > or an RT task preempted the old rq->curr, not absolute irq/rt length.
    As far as my understanding, core's capacity = IRQ + DEADLINE + RT +
    CFS. For a certain time period, all cfs tasks preempt each other
    inside CFS's utilization. So the sleeping on refaults is counted in.
    >
    > (Btw, such preemption periods, in addition to being deducted from
    > memory stalls, should probably also be added to CPU contention stalls,
    > to make CPU pressure reporting more accurate as well.)

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