linux-kernel - Re: RCU NOHZ, tsc, and clock

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Date:	Tue, 13 Nov 2012 10:18:30 -0500
From:	Prarit Bhargava <prarit@...hat.com>
To:	John Stultz <johnstul@...ibm.com>
CC:	paulmck@...ux.vnet.ibm.com,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Marcelo Tosatti <mtosatti@...hat.com>
Subject: Re: RCU NOHZ, tsc, and clock_gettime



On 11/12/2012 06:27 PM, John Stultz wrote:

> Hey Prarit,
>     Just back from being on leave, and wanted to check in on this. Did you ever
> get to run with an increase sample size to see how that affected things?  Its
> exactly your point that the non-NOHZ case could align the execution of a short
> run in a way that you always see good results, where as with NOHZ the alignment
> might not be the same, so you see periodic delays from timer interrupts, etc.
> 
> Anyway, let me know if this got resolved or not.

Hey John,

I never did narrow this down, although this "disappears" with the move to the
lower resolution patches in upstream.  I have not, however, done any testing to
see if the situation is actually resolved or if we just reduced the problem by a
factor of 1000 ;)

P.
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