linux-kernel - Re: [PATCH 7/8] sched, net: Fixup busy_loop_us

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Date:	Thu, 28 Nov 2013 18:49:00 +0200
From:	Eliezer Tamir <eliezer.tamir@...ux.intel.com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Arjan van de Ven <arjan@...ux.intel.com>, lenb@...nel.org,
	rjw@...ysocki.net, David Miller <davem@...emloft.net>,
	rui.zhang@...el.com, jacob.jun.pan@...ux.intel.com,
	Mike Galbraith <bitbucket@...ine.de>,
	Ingo Molnar <mingo@...nel.org>, hpa@...or.com,
	Thomas Gleixner <tglx@...utronix.de>
CC:	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH 7/8] sched, net: Fixup busy_loop_us_clock()

On 26/11/2013 17:57, Peter Zijlstra wrote:
> 
> Replace sched_clock() usage with local_clock() which has a bounded
> drift between CPUs (<2 jiffies).
> 

Peter,

I have tested this patch and I see a performance regression of about
1.5%.

Maybe it would be better, rather then testing in the fast path, to
simply disallow busy polling altogether when sched_clock_stable is
not true?

Thanks,
Eliezer
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