From: Peter Zijlstra <peterz@infradead.org>
To: mingo@kernel.org, tglx@linutronix.de
Cc: linux-kernel@vger.kernel.org, juri.lelli@redhat.com,
vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de,
paulmck@kernel.org, frederic@kernel.org, peterz@infradead.org
Subject: [PATCH 1/6] sched: Fix ttwu_queue_cond()
Date: Mon, 15 Jun 2020 14:56:55 +0200 [thread overview]
Message-ID: <20200615131143.130326165@infradead.org> (raw)
In-Reply-To: 20200615125654.678940605@infradead.org
Where the condition:
!cpus_share_cache(smp_processor_id(), cpu)
already implies 'cpu != smp_processor_id()', because a CPU always
shares cache with itself, the secondary condition added in commit:
2ebb17717550 ("sched/core: Offload wakee task activation if it the wakee is descheduling")
voids that implication, resulting in attempting to do local wake-ups
through the queue mechanism.
Fixes: 2ebb17717550 ("sched/core: Offload wakee task activation if it the wakee is descheduling")
Reported-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Paul E. McKenney <paulmck@kernel.org>
---
kernel/sched/core.c | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2356,11 +2356,22 @@ bool cpus_share_cache(int this_cpu, int
static inline bool ttwu_queue_cond(int cpu, int wake_flags)
{
+ int this_cpu = smp_processor_id();
+
+ /*
+ * Only ever queue for remote wakeups. The on_cpu case can only ever
+ * happen remotely, and for the normal case it makes no sense to
+ * involve IPIs here, and would be broken, as many architectures cannot
+ * trivially IPI self in any case.
+ */
+ if (cpu == this_cpu)
+ return false;
+
/*
* If the CPU does not share cache, then queue the task on the
* remote rqs wakelist to avoid accessing remote data.
*/
- if (!cpus_share_cache(smp_processor_id(), cpu))
+ if (!cpus_share_cache(this_cpu, cpu))
return true;
/*
next prev parent reply other threads:[~2020-06-15 13:18 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-15 12:56 [PATCH 0/6] sched: TTWU, IPI, and assorted stuff Peter Zijlstra
2020-06-15 12:56 ` Peter Zijlstra [this message]
2020-06-15 13:34 ` [PATCH 1/6] sched: Fix ttwu_queue_cond() Peter Zijlstra
2020-06-15 16:45 ` Paul E. McKenney
2020-06-15 22:58 ` Paul E. McKenney
2020-06-22 9:11 ` Mel Gorman
2020-06-22 9:41 ` Peter Zijlstra
2020-06-15 12:56 ` [PATCH 2/6] sched: Verify some SMP assumptions Peter Zijlstra
2020-06-15 12:56 ` [PATCH 3/6] sched: s/WF_ON_RQ/WQ_ON_CPU/ Peter Zijlstra
2020-06-22 9:13 ` Mel Gorman
2020-06-15 12:56 ` [PATCH 4/6] smp, irq_work: Continue smp_call_function*() and irq_work*() integration Peter Zijlstra
2020-06-15 12:56 ` [PATCH 5/6] irq_work: Cleanup Peter Zijlstra
2020-06-16 15:16 ` Petr Mladek
2020-06-15 12:57 ` [PATCH 6/6] smp: Cleanup smp_call_function*() Peter Zijlstra
2020-06-15 14:34 ` Jens Axboe
2020-06-15 16:04 ` Daniel Thompson
2020-06-17 8:23 ` Christoph Hellwig
2020-06-17 9:00 ` Peter Zijlstra
2020-06-17 11:04 ` Peter Zijlstra
2020-06-18 6:51 ` Christoph Hellwig
2020-06-18 16:25 ` Peter Zijlstra
2020-06-15 16:23 ` [PATCH 0/6] sched: TTWU, IPI, and assorted stuff Paul E. McKenney
2020-06-15 16:40 ` Peter Zijlstra
2020-06-15 17:21 ` Paul E. McKenney
2020-06-15 19:11 ` Peter Zijlstra
2020-06-15 19:55 ` Paul E. McKenney
2020-06-16 16:31 ` Paul E. McKenney
2020-06-16 17:04 ` Peter Zijlstra
2020-06-16 17:17 ` Peter Zijlstra
2020-06-16 17:53 ` Paul E. McKenney
2020-06-19 13:44 ` Peter Zijlstra
2020-06-19 17:20 ` Paul E. McKenney
2020-06-19 17:48 ` Paul E. McKenney
2020-06-19 18:11 ` Peter Zijlstra
2020-06-19 18:46 ` Paul E. McKenney
2020-06-20 18:46 ` Paul E. McKenney
2020-06-16 17:51 ` Paul E. McKenney
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