From: Yuyang Du <yuyang.du@intel.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Chris Wilson <chris@chris-wilson.co.uk>,
Andrey Ryabinin <aryabinin@virtuozzo.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Mike Galbraith <efault@gmx.de>,
Thomas Gleixner <tglx@linutronix.de>,
bsegall@google.com, morten.rasmussen@arm.com, pjt@google.com,
steve.muckle@linaro.org, linux-kernel@vger.kernel.org,
kernel@kyup.com
Subject: Re: [PATCH] sched/fair: Fix cfs_rq avg tracking underflow
Date: Fri, 17 Jun 2016 10:01:09 +0800 [thread overview]
Message-ID: <20160617020109.GQ8105@intel.com> (raw)
In-Reply-To: <20160617091948.GJ30927@twins.programming.kicks-ass.net>
On Fri, Jun 17, 2016 at 11:19:48AM +0200, Peter Zijlstra wrote:
> +/*
> + * Unsigned subtract 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 sub_positive(_ptr, _val) do { \
> + typeof(_ptr) ptr = (_ptr); \
> + typeof(*ptr) val = (_val); \
> + typeof(*ptr) res, var = READ_ONCE(*ptr); \
> + res = var - val; \
> + if (res > var) \
> + res = 0; \
> + WRITE_ONCE(*ptr, res); \
> +} while (0)
> +
maybe sub_nonnegative() or sub_til_zero() ...
I wonder whether it is the if statement finally allows GCC to 'registerize'
load_avg, and I almost tried it...
next prev parent reply other threads:[~2016-06-17 9:57 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-09 9:01 Divide-by-zero in post_init_entity_util_avg Chris Wilson
2016-06-09 1:33 ` Yuyang Du
2016-06-09 13:07 ` Peter Zijlstra
2016-06-12 22:25 ` Yuyang Du
2016-06-14 11:25 ` [tip:sched/core] sched/fair: Fix post_init_entity_util_avg() serialization tip-bot for Peter Zijlstra
2016-06-16 8:50 ` Divide-by-zero in post_init_entity_util_avg Peter Zijlstra
2016-06-16 12:25 ` Peter Zijlstra
2016-06-16 16:16 ` Peter Zijlstra
2016-06-17 8:16 ` Andrey Ryabinin
2016-06-17 8:23 ` Peter Zijlstra
2016-06-17 9:19 ` [PATCH] sched/fair: Fix cfs_rq avg tracking underflow Peter Zijlstra
2016-06-17 2:01 ` Yuyang Du [this message]
2016-06-20 13:24 ` [tip:sched/urgent] " tip-bot for Peter Zijlstra
2016-06-09 10:29 ` Divide-by-zero in post_init_entity_util_avg Peter Zijlstra
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