linux-kernel - Re: [PATCH RFC/RFB] x86_64, i386: interrupt dispatch changes

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Message-Id: <1226615039.3343.53.camel@calx>
Date:	Thu, 13 Nov 2008 16:23:59 -0600
From:	Matt Mackall <mpm@...enic.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Alexander van Heukelum <heukelum@...tmail.fm>,
	Ingo Molnar <mingo@...e.hu>, Andi Kleen <andi@...stfloor.org>,
	Cyrill Gorcunov <gorcunov@...il.com>,
	Alexander van Heukelum <heukelum@...lshack.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>, lguest@...abs.org,
	jeremy@...source.com, Steven Rostedt <srostedt@...hat.com>,
	Mike Travis <travis@....com>
Subject: Re: [PATCH RFC/RFB] x86_64, i386: interrupt dispatch changes

On Mon, 2008-11-10 at 21:00 -0800, H. Peter Anvin wrote:
> Okay, after spending most of the day trying to get something that isn't
> completely like white noise (interesting problem, otherwise I'd have
> given up long ago) I did, eventually, come up with something that looks
> like it's significant.  I did a set of multiple runs, and am looking for
> the "waterfall points" in the cumulative statistics.
> 
> http://www.zytor.com/~hpa/baseline-hpa-3000-3600.pdf
> 
> This particular set of data points was gathered on a 64-bit kernel, so I
> didn't try the segment technique.
> 
> It looks to me that the collection of red lines is enough to the left of
> the black ones that one can assume there is a significant effect,
> probably by about a cache miss worth of time.

This graph is a little confusing. Is the area under each curve here
supposed to be a constant?

Is this latency from all interrupts as seen by userspace? Or does a
particular interrupt dominate?

-- 
Mathematics is the supreme nostalgia of our time.

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