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Date: Mon, 15 Mar 2010 10:10:14 +0100 From: Oleg Nesterov <oleg@...hat.com> To: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu> Cc: Ben Blum <bblum@...gle.com>, Jiri Slaby <jirislaby@...il.com>, Lai Jiangshan <laijs@...fujitsu.com>, Li Zefan <lizf@...fujitsu.com>, Miao Xie <miaox@...fujitsu.com>, Paul Menage <menage@...gle.com>, "Rafael J. Wysocki" <rjw@...k.pl>, Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org Subject: [PATCH 3/6] move_task_off_dead_cpu: remove retry logic The previous patch preserved the retry logic, but it looks unneeded. __migrate_task() can only fail if we raced with migration after we dropped the lock, but in this case the caller of set_cpus_allowed/etc must initiate migration itself if ->on_rq == T. We already fixed p->cpus_allowed, the changes in active/online masks must be visible to racer, it should migrate the task to online cpu correctly. Signed-off-by: Oleg Nesterov <oleg@...hat.com> --- kernel/sched.c | 13 ++++++------- 1 file changed, 6 insertions(+), 7 deletions(-) --- 34-rc1/kernel/sched.c~2_XXX_MTODC_DONT_RETRY 2010-03-15 09:40:31.000000000 +0100 +++ 34-rc1/kernel/sched.c 2010-03-15 09:40:44.000000000 +0100 @@ -5517,7 +5517,7 @@ static void move_task_off_dead_cpu(int d struct rq *rq = cpu_rq(dead_cpu); int needs_cpu, dest_cpu; unsigned long flags; -again: + local_irq_save(flags); raw_spin_lock(&rq->lock); @@ -5525,14 +5525,13 @@ again: if (needs_cpu) dest_cpu = select_fallback_rq(dead_cpu, p); raw_spin_unlock(&rq->lock); - - /* It can have affinity changed while we were choosing. */ + /* + * It can only fail if we race with set_cpus_allowed(), + * in the racer should migrate the task anyway. + */ if (needs_cpu) - needs_cpu = !__migrate_task(p, dead_cpu, dest_cpu); + __migrate_task(p, dead_cpu, dest_cpu); local_irq_restore(flags); - - if (unlikely(needs_cpu)) - goto again; } /* -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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