Messages in this thread Patch in this message | | | Date | Thu, 28 May 2015 13:05:14 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH RESEND] sched: prefer an idle cpu vs an idle sibling for BALANCE_WAKE |
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So maybe you want something like the below; that cures the thing Morten raised, and we continue looking for sd, even after we found affine_sd.
It also avoids the pointless idle_cpu() check Mike raised by making select_idle_sibling() return -1 if it doesn't find anything.
Then it continues doing the full balance IFF sd was set, which is keyed off of sd->flags.
And note (as Mike already said), BALANCE_WAKE does _NOT_ look for idle CPUs, it looks for the least loaded CPU. And its damn expensive.
Rewriting this entire thing is somewhere on the todo list :/
--- kernel/sched/fair.c | 36 +++++++++++++++++++++++------------- 1 file changed, 23 insertions(+), 13 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index d597aea43030..7330fb4fea9c 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -1385,8 +1385,13 @@ static void task_numa_compare(struct task_numa_env *env, * One idle CPU per node is evaluated for a task numa move. * Call select_idle_sibling to maybe find a better one. */ - if (!cur) - env->dst_cpu = select_idle_sibling(env->p, env->dst_cpu); + if (!cur) { + int cpu = select_idle_sibling(env->p, env->dst_cpu); + if (cpu < 0) + cpu = env->dst_cpu; + + env->dst_cpu = cpu; + } assign: task_numa_assign(env, cur, imp); @@ -4951,16 +4956,15 @@ static int select_idle_sibling(struct task_struct *p, int target) goto next; } - target = cpumask_first_and(sched_group_cpus(sg), + return cpumask_first_and(sched_group_cpus(sg), tsk_cpus_allowed(p)); - goto done; next: sg = sg->next; } while (sg != sd->groups); } -done: - return target; + return -1; } + /* * get_cpu_usage returns the amount of capacity of a CPU that is used by CFS * tasks. The unit of the return value must be the one of capacity so we can @@ -5022,22 +5026,28 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f * If both cpu and prev_cpu are part of this domain, * cpu is a valid SD_WAKE_AFFINE target. */ - if (want_affine && (tmp->flags & SD_WAKE_AFFINE) && - cpumask_test_cpu(prev_cpu, sched_domain_span(tmp))) { + if (want_affine && !affine_sd && + (tmp->flags & SD_WAKE_AFFINE) && + cpumask_test_cpu(prev_cpu, sched_domain_span(tmp))) affine_sd = tmp; - break; - } if (tmp->flags & sd_flag) sd = tmp; + else if (!want_affine || (want_affine && affine_sd)) + break; } - if (affine_sd && cpu != prev_cpu && wake_affine(affine_sd, p, sync)) + if (affine_sd && cpu != prev_cpu && wake_affine(affine_sd, p, sync)) { prev_cpu = cpu; + sd = NULL; /* WAKE_AFFINE trumps BALANCE_WAKE */ + } if (sd_flag & SD_BALANCE_WAKE) { - new_cpu = select_idle_sibling(p, prev_cpu); - goto unlock; + int tmp = select_idle_sibling(p, prev_cpu); + if (tmp >= 0) { + new_cpu = tmp; + goto unlock; + } } while (sd) {
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