From: Vincent Guittot <vincent.guittot@linaro.org>
To: andrea.parri@amarulasolutions.com
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH] sched/fair: Clean up comment in nohz_idle_balance()
Date: Tue, 27 Nov 2018 15:41:42 +0100 [thread overview]
Message-ID: <CAKfTPtBQx64Ovc9_khCi33YFTuXG=ekzU=XOB5Fz2oXHt_cCHA@mail.gmail.com> (raw)
In-Reply-To: <20181127110110.5533-1-andrea.parri@amarulasolutions.com>
On Tue, 27 Nov 2018 at 12:01, Andrea Parri
<andrea.parri@amarulasolutions.com> wrote:
>
> Concerning the comment associated to the atomic_fetch_andnot() in
> nohz_idle_balance(), Vincent explains [1]:
>
> "[...] the comment is useless and can be removed [...] it was
> referring to a line code above the comment that was present in
> a previous iteration of the patchset. This line disappeared in
> final version but the comment has stayed."
>
> So remove the comment.
>
> Vincent also points out that the full ordering associated to the
> atomic_fetch_andnot() primitive could be relaxed, but this patch
> insists on the current more conservative/fully ordered solution:
>
> "Performance" isn't a concern, stay away from "correctness"/subtle
> relaxed (re)ordering if possible..., just make sure not to confuse
> the next reader with misleading/out-of-date comments.
>
> [1] http://lkml.kernel.org/r/CAKfTPtBjA-oCBRkO6__npQwL3+HLjzk7riCcPU1R7YdO-EpuZg@mail.gmail.com
>
> Suggested-by: Vincent Guittot <vincent.guittot@linaro.org>
> Signed-off-by: Andrea Parri <andrea.parri@amarulasolutions.com>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Vincent Guittot <vincent.guittot@linaro.org>
Looks good to me
> ---
> kernel/sched/fair.c | 4 +---
> 1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index ac855b2f47746..db514993565b2 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -9533,9 +9533,7 @@ static bool nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle)
> return false;
> }
>
> - /*
> - * barrier, pairs with nohz_balance_enter_idle(), ensures ...
> - */
> + /* could be _relaxed() */
> flags = atomic_fetch_andnot(NOHZ_KICK_MASK, nohz_flags(this_cpu));
> if (!(flags & NOHZ_KICK_MASK))
> return false;
> --
> 2.17.1
>
next prev parent reply other threads:[~2018-11-27 14:41 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-27 11:01 [PATCH] sched/fair: Clean up comment in nohz_idle_balance() Andrea Parri
2018-11-27 14:41 ` Vincent Guittot [this message]
2018-12-11 15:30 ` [tip:locking/core] " tip-bot for Andrea Parri
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