Messages in this thread | | | Subject | Re: [PATCH v3 1/7] sched: limit cpu search in select_idle_cpu | From | Parth Shah <> | Date | Sat, 29 Jun 2019 00:17:49 +0530 |
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On 6/27/19 6:59 AM, subhra mazumdar wrote: > Put upper and lower limit on cpu search of select_idle_cpu. The lower limit > is amount of cpus in a core while upper limit is twice that. This ensures > for any architecture we will usually search beyond a core. The upper limit > also helps in keeping the search cost low and constant. > > Signed-off-by: subhra mazumdar <subhra.mazumdar@oracle.com> > --- > kernel/sched/fair.c | 15 +++++++++++---- > 1 file changed, 11 insertions(+), 4 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index f35930f..b58f08f 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -6188,7 +6188,7 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t > u64 avg_cost, avg_idle; > u64 time, cost; > s64 delta; > - int cpu, nr = INT_MAX; > + int cpu, limit, floor, nr = INT_MAX; > > this_sd = rcu_dereference(*this_cpu_ptr(&sd_llc)); > if (!this_sd) > @@ -6206,10 +6206,17 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t > > if (sched_feat(SIS_PROP)) { > u64 span_avg = sd->span_weight * avg_idle; > - if (span_avg > 4*avg_cost) > + floor = cpumask_weight(topology_sibling_cpumask(target)); > + if (floor < 2) > + floor = 2; > + limit = floor << 1;
Is upper limit an experimental value only or it has any arch specific significance? Because, AFAIU, systems like POWER9 might have benefit for searching for 4-cores due to its different cache model. So it can be tuned for arch specific builds then.
Also variable names can be changed for better readability. floor -> weight_clamp_min limit -> weight_clamp_max or something similar
> + if (span_avg > floor*avg_cost) { > nr = div_u64(span_avg, avg_cost); > - else > - nr = 4; > + if (nr > limit) > + nr = limit; > + } else { > + nr = floor; > + } > } > > time = local_clock(); >
Best, Parth
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