On Sun, Nov 09, 2014 at 05:07:00PM +0300, Kirill Tkhai wrote: > > I've complained about an unrelated issue in that part of the code > > a while back (https://lkml.org/lkml/2014/5/12/508) which PeterZ > > ended up fixing (https://lkml.org/lkml/2014/5/21/428) but it seems > > that both of us forgot to follow up on that and the fix never got > > upstream.
Argh, sorry for that! > The bellow is equal to the patch suggested by Peter. > > The only thing, I'm doubt, is about the comparison of cpus instead of nids. > Should task_numa_compare() be able to be called with src_nid == dst_nid > like this may happens now?! Maybe better, we should change task_numa_migrate() > and check for env.dst_nid != env.src.nid. > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 826fdf3..c18129e 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -1380,6 +1380,8 @@ static void task_numa_find_cpu(struct task_numa_env > *env, > /* Skip this CPU if the source task cannot migrate */ > if (!cpumask_test_cpu(cpu, tsk_cpus_allowed(env->p))) > continue; > + if (cpu == env->src_cpu) > + continue; > > env->dst_cpu = cpu; > task_numa_compare(env, taskimp, groupimp); Not quite the same, current can still get migrated to another cpu than env->src_cpu, at which point we can still end up selecting ourselves. How about the below instead, that is pretty much the old patch, but with a nice comment. --- Subject: sched, numa: Avoid selecting oneself as swap target From: Peter Zijlstra <[email protected]> Date: Mon Nov 10 10:54:35 CET 2014 Because the whole numa task selection stuff runs with preemption enabled (its long and expensive) we can end up migrating and selecting oneself as a swap target. This doesn't really work out well -- we end up trying to acquire the same lock twice for the swap migrate -- so avoid this. Cc: Rik van Riel <[email protected]> Tested-by: Sasha Levin <[email protected]> Reported-by: Sasha Levin <[email protected]> Signed-off-by: Peter Zijlstra (Intel) <[email protected]> --- kernel/sched/fair.c | 7 +++++++ 1 file changed, 7 insertions(+) --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -1268,6 +1268,13 @@ static void task_numa_compare(struct tas raw_spin_unlock_irq(&dst_rq->lock); /* + * Because we have preemption enabled we can get migrated around and + * end try selecting ourselves (current == env->p) as a swap candidate. + */ + if (cur == env->p) + goto unlock; + + /* * "imp" is the fault differential for the source task between the * source and destination node. Calculate the total differential for * the source task and potential destination task. The more negative -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
