linux-kernel - Re: [PATCH 09/10] sched: task_sched_runtime introduce micro optimization

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Date:	Wed, 01 May 2013 14:55:33 -0400
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	Paul Turner <pjt@...gle.com>
CC:	Peter Zijlstra <peterz@...radead.org>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Olivier Langlois <olivier@...llion01.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	David Miller <davem@...emloft.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Subject: Re: [PATCH 09/10] sched: task_sched_runtime introduce micro optimization

> Stronger:
> 
> +#ifdef CONFIG_64BIT
> +       if (!p->on_cpu)
> +               return p->se.sum_exec_runtime;
> +#endif
> 
> [ Or !p->on_cpu || !add_delta ].
> 
> We can take the racy read versus p->on_cpu since:
>   If we race with it leaving cpu: we take lock, we're correct
>   If we race with it entering cpu: unaccounted time ---> 0, this is
> indistinguishable from the read occurring a few cycles earlier.

OK, agreed. That's nice.


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