Re: [PATCH v3] sched/numa: add per-process numa_balancing
From: Peter Zijlstra <peterz@infradead.org>
Date: 2022-01-12 14:44:17
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linux-doc, linux-fsdevel, lkml
On Mon, Dec 06, 2021 at 10:45:28AM +0800, Gang Li wrote:
This patch add a new api PR_NUMA_BALANCING in prctl. A large number of page faults will cause performance loss when numa balancing is performing. Thus those processes which care about worst-case performance need numa balancing disabled. Others, on the contrary, allow a temporary performance loss in exchange for higher average performance, so enable numa balancing is better for them. Numa balancing can only be controlled globally by /proc/sys/kernel/numa_balancing. Due to the above case, we want to disable/enable numa_balancing per-process instead. Add numa_balancing under mm_struct. Then use it in task_tick_fair. Set per-process numa balancing: prctl(PR_NUMA_BALANCING, PR_SET_NUMAB_DISABLE); //disable prctl(PR_NUMA_BALANCING, PR_SET_NUMAB_ENABLE); //enable prctl(PR_NUMA_BALANCING, PR_SET_NUMAB_DEFAULT); //follow global
This seems to imply you can prctl(ENABLE) even if the global is disabled, IOW sched_numa_balancing is off.
quoted hunk ↗ jump to hunk
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 884f29d07963..2980f33ac61f 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c@@ -11169,8 +11169,12 @@ static void task_tick_fair(struct rq *rq, struct task_struct *curr, int queued) entity_tick(cfs_rq, se, queued); } - if (static_branch_unlikely(&sched_numa_balancing)) +#ifdef CONFIG_NUMA_BALANCING + if (curr->mm && (curr->mm->numab_enabled == NUMAB_ENABLED + || (static_branch_unlikely(&sched_numa_balancing) + && curr->mm->numab_enabled == NUMAB_DEFAULT))) task_tick_numa(rq, curr); +#endif update_misfit_status(curr, rq); update_overutilized_status(task_rq(curr));
There's just about everything wrong there... not least of all the horrific coding style.