From: Peter Zijlstra <peterz@infradead.org>
To: Vincent Guittot <vincent.guittot@linaro.org>
Cc: mingo@kernel.org, linux-kernel@vger.kernel.org,
dietmar.eggemann@arm.com, yuyang.du@intel.com,
Morten.Rasmussen@arm.com, linaro-kernel@lists.linaro.org,
pjt@google.com, bsegall@google.com, kernellwp@gmail.com
Subject: Re: [PATCH 4/6 v5] sched: propagate load during synchronous attach/detach
Date: Wed, 26 Oct 2016 12:54:07 +0200 [thread overview]
Message-ID: <20161026105407.GE3102@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <1476695653-12309-5-git-send-email-vincent.guittot@linaro.org>
On Mon, Oct 17, 2016 at 11:14:11AM +0200, Vincent Guittot wrote:
> /*
> + * Signed add and clamp on underflow.
> + *
> + * Explicitly do a load-store to ensure the intermediate value never hits
> + * memory. This allows lockless observations without ever seeing the negative
> + * values.
> + */
> +#define add_positive(_ptr, _val) do { \
> + typeof(_ptr) ptr = (_ptr); \
> + typeof(_val) res, val = (_val); \
> + typeof(*ptr) var = READ_ONCE(*ptr); \
> + res = var + val; \
> + if (res < 0) \
> + res = 0; \
I think this is broken, and inconsistent with sub_positive().
The thing is, util_avg, on which you use this, is an unsigned type.
Checking for unsigned underflow can be done by comparing against either
one of the terms.
> + WRITE_ONCE(*ptr, res); \
> +} while (0)
> + add_positive(&cfs_rq->avg.util_avg, delta);
next prev parent reply other threads:[~2016-10-26 10:54 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-17 9:14 [PATCH 0/6 v5] sched: reflect sched_entity move into task_group's load Vincent Guittot
2016-10-17 9:14 ` [PATCH 1/6 v5] sched: factorize attach entity Vincent Guittot
2016-10-17 9:14 ` [PATCH 2/6 v5] sched: fix hierarchical order in rq->leaf_cfs_rq_list Vincent Guittot
2016-10-17 9:14 ` [PATCH 3/6 v5] sched: factorize PELT update Vincent Guittot
2016-10-26 11:41 ` Peter Zijlstra
2016-10-26 12:56 ` Vincent Guittot
2016-10-17 9:14 ` [PATCH 4/6 v5] sched: propagate load during synchronous attach/detach Vincent Guittot
2016-10-21 12:19 ` Dietmar Eggemann
2016-10-26 7:05 ` Vincent Guittot
2016-10-26 11:16 ` Peter Zijlstra
2016-10-26 12:31 ` Vincent Guittot
2016-10-26 10:54 ` Peter Zijlstra [this message]
2016-10-26 12:31 ` Vincent Guittot
2016-10-26 14:28 ` Peter Zijlstra
2016-10-26 18:40 ` Vincent Guittot
2016-10-26 11:45 ` Peter Zijlstra
2016-10-17 9:14 ` [PATCH 5/6 v5] sched: propagate asynchrous detach Vincent Guittot
2016-10-17 9:14 ` [PATCH 6/6 v5] sched: fix task group initialization Vincent Guittot
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