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Date: Wed, 13 Aug 2014 13:11:12 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>, Rik van Riel <riel@redhat.com>,
        linux-kernel@vger.kernel.org,
        Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>,
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        Andrew Morton <akpm@linux-foundation.org>,
        Sanjay Rao <srao@redhat.com>, Larry Woodman <lwoodman@redhat.com>
Subject: Re: [PATCH RFC] time: drop do_sys_times spinlock
Message-ID: <20140813111112.GJ9918@twins.programming.kicks-ass.net>
References: <20140812142539.01851e52@annuminas.surriel.com>
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On Wed, Aug 13, 2014 at 08:59:50AM +0200, Mike Galbraith wrote:
=20
> I was told that clock_gettime(CLOCK_PROCESS_CPUTIME_ID) has scalability
> issues on BIG boxen

> I'm sure the real clock_gettime() using proggy that gummed up a ~1200
> core box for "a while" wasn't the testcase below, which will gum it up
> for a long while, but looks to me like using CLOCK_PROCESS_CPUTIME_ID
> from LOTS of threads is a "Don't do that, it'll hurt a LOT".

Yes, don't do that. Its unavoidably slow and bad.

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