Messages in this thread | | | Subject | Re: [PATCH V3 1/2] sched/fair: Fix load_balance() affinity redo path | From | Dietmar Eggemann <> | Date | Mon, 22 May 2017 10:48:59 +0100 |
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On 19/05/17 14:31, Dietmar Eggemann wrote: > On 18/05/17 20:36, Jeffrey Hugo wrote: > > [...] > >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >> index d711093..a5d41b1 100644 >> --- a/kernel/sched/fair.c >> +++ b/kernel/sched/fair.c >> @@ -8220,7 +8220,24 @@ static int load_balance(int this_cpu, struct rq *this_rq, >> /* All tasks on this runqueue were pinned by CPU affinity */ >> if (unlikely(env.flags & LBF_ALL_PINNED)) { >> cpumask_clear_cpu(cpu_of(busiest), cpus); >> - if (!cpumask_empty(cpus)) { >> + /* >> + * dst_cpu is not a valid busiest cpu in the following >> + * check since load cannot be pulled from dst_cpu to be >> + * put on dst_cpu. >> + */ >> + cpumask_clear_cpu(env.dst_cpu, cpus); >> + /* >> + * Go back to "redo" iff the load-balance cpumask >> + * contains other potential busiest cpus for the >> + * current sched domain. >> + */ >> + if (cpumask_intersects(cpus, sched_domain_span(env.sd))) { >> + /* >> + * Now that the check has passed, reenable >> + * dst_cpu so that load can be calculated on >> + * it in the redo path. >> + */ >> + cpumask_set_cpu(env.dst_cpu, cpus); > > IMHO, this will work nicely and its way easier.
This was too quick ... if we still have other potential dst cpus available and cpu_of(busiest) is the latest src cpu then this will fail.
It does work on sd with 'group_weight == 1', e.g. your MC sd 'sd->child == NULL'.
But IMHO 'group_imbalance' propagation has to work on higher sd levels as well.
> Another idea might be to check if the LBF_ALL_PINNED is set when we > check if we should clean the imbalance flag. > > @@ -8307,14 +8307,13 @@ static int load_balance(int this_cpu, struct rq *this_rq, > * We reach balance although we may have faced some affinity > * constraints. Clear the imbalance flag if it was set. > */ > - if (sd_parent) { > + if (sd_parent && !(env.flags & LBF_ALL_PINNED)) { > int *group_imbalance = &sd_parent->groups->sgc->imbalance; > > if (*group_imbalance) > *group_imbalance = 0; > }
[...]
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