Message-ID: <51816525.7060305@gmail.com>
Date: Wed, 01 May 2013 14:55:33 -0400
From: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
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To: Paul Turner <pjt@google.com>
CC: Peter Zijlstra <peterz@infradead.org>,
        KOSAKI Motohiro <kosaki.motohiro@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Olivier Langlois <olivier@trillion01.com>,
        Martin Schwidefsky <schwidefsky@de.ibm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        David Miller <davem@davemloft.net>,
        Thomas Gleixner <tglx@linutronix.de>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Ingo Molnar <mingo@kernel.org>,
        KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Subject: Re: [PATCH 09/10] sched: task_sched_runtime introduce micro optimization
References: <1367291838-5490-1-git-send-email-kosaki.motohiro@gmail.com> <1367291838-5490-10-git-send-email-kosaki.motohiro@gmail.com> <20130501110047.GD28253@dyad.programming.kicks-ass.net> <CAPM31RJ0HWQCU=oDnd=iTyEZzsTS3xSe89rmgVK8cd8umAC5BQ@mail.gmail.com>
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> 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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