linux-kernel - Re: [PATCH RFC] time: drop do_sys

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Message-ID: <20140813111112.GJ9918@twins.programming.kicks-ass.net>
Date:	Wed, 13 Aug 2014 13:11:12 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Mike Galbraith <umgwanakikbuti@...il.com>
Cc:	Oleg Nesterov <oleg@...hat.com>, Rik van Riel <riel@...hat.com>,
	linux-kernel@...r.kernel.org,
	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
	Frank Mayhar <fmayhar@...gle.com>,
	Frederic Weisbecker <fweisbec@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Sanjay Rao <srao@...hat.com>,
	Larry Woodman <lwoodman@...hat.com>
Subject: Re: [PATCH RFC] time: drop do_sys_times spinlock

On Wed, Aug 13, 2014 at 08:59:50AM +0200, Mike Galbraith wrote:
 
> 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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