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From: Andrea Parri <andrea.parri@amarulasolutions.com>
To: Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>
Cc: linux-kernel@vger.kernel.org
Subject: [Question] atomic_fetch_andnot() in nohz_idle_balance()
Date: Wed, 21 Nov 2018 23:34:53 +0100	[thread overview]
Message-ID: <20181121223453.GA4016@andrea> (raw)

Hi,

The comment for the atomic_fetch_andnot() in nohz_idle_balance() says:

  "barrier, pairs with nohz_balance_enter_idle(), ensures ..."

which, well, does sound a note of warning... ;-)

I see that nohz_balance_enter_idle() has an smp_mb__after_atomic() but
the comment for the latter suggests that this barrier is pairing with
the smp_mb() in _nohz_idle_balance().

So, what is the intended pairing barrier for the atomic_fetch_andnot()?
what (which memory accesses) do you want "to order" here?

Thanks,
  Andrea

             reply	other threads:[~2018-11-21 22:35 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-21 22:34 Andrea Parri [this message]
2018-11-26  9:30 ` [Question] atomic_fetch_andnot() in nohz_idle_balance() Peter Zijlstra
2018-11-26 11:37   ` Vincent Guittot
2018-11-26 20:44     ` Andrea Parri
2018-11-27  9:01       ` Vincent Guittot
2018-11-27 10:59         ` Andrea Parri

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