From: Peter Zijlstra <peterz@infradead.org>
To: Andrea Parri <andrea.parri@amarulasolutions.com>
Cc: Ingo Molnar <mingo@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
linux-kernel@vger.kernel.org
Subject: Re: [Question] atomic_fetch_andnot() in nohz_idle_balance()
Date: Mon, 26 Nov 2018 10:30:51 +0100 [thread overview]
Message-ID: <20181126093051.GV2131@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20181121223453.GA4016@andrea>
On Wed, Nov 21, 2018 at 11:34:53PM +0100, Andrea Parri wrote:
> 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?
I can't seem to make sense of that comment either; the best I can come
up with is that it would order the prior NOHZ_KICK_MASK load vs us then
changing it.
But that would order against kick_ilb(), not enter_idle.
Vincent?
next prev parent reply other threads:[~2018-11-26 9:31 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-21 22:34 [Question] atomic_fetch_andnot() in nohz_idle_balance() Andrea Parri
2018-11-26 9:30 ` Peter Zijlstra [this message]
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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