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Date: Tue, 16 May 2017 10:14:53 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Dave Kleikamp <dave.kleikamp@oracle.com>
Cc: LKML <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@redhat.com>
Subject: Re: [PATCH RESEND 1/1] sched/rt: minimize rq->lock contention in,
 do_sched_rt_period_timer()
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On Mon, May 15, 2017 at 02:14:13PM -0500, Dave Kleikamp wrote:
> With CONFIG_RT_GROUP_SCHED defined, do_sched_rt_period_timer() sequentially
> takes each cpu's rq->lock. On a large, busy system, the cumulative time it
> takes to acquire each lock can be excessive, even triggering a watchdog
> timeout.
> 
> If rt_rq_rt_time and rt_rq->rt_nr_running are both zero, this function does
> nothing while holding the lock, so don't bother taking it at all.

Indeed, thanks Dave!