From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eliezer Tamir <eliezer.tamir@linux.intel.com>
Subject: Re: [PATCH 7/8] sched, net: Fixup busy_loop_us_clock()
Date: Thu, 28 Nov 2013 18:49:00 +0200
Message-ID: <529773FC.6020707@linux.intel.com>
References: <20131126155743.116756708@infradead.org> <20131126160815.293633156@infradead.org>
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To: Peter Zijlstra <peterz@infradead.org>, Arjan van de Ven <arjan@linux.intel.com>, lenb@kernel.org, rjw@rjwysocki.net, David Miller <davem@davemloft.net>, rui.zhang@intel.com, jacob.jun.pan@linux.intel.com, Mike Galbraith <bitbucket@online.de>, Ingo Molnar <mingo@kernel.org>, hpa@zytor.com, Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org

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