Subject: Re: [PATCH RFC/RFB] x86_64, i386: interrupt dispatch changes
From: Matt Mackall <mpm@selenic.com>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Alexander van Heukelum <heukelum@fastmail.fm>, Ingo Molnar <mingo@elte.hu>,
       Andi Kleen <andi@firstfloor.org>, Cyrill Gorcunov <gorcunov@gmail.com>,
       Alexander van Heukelum <heukelum@mailshack.com>,
       LKML <linux-kernel@vger.kernel.org>,
       Thomas Gleixner <tglx@linutronix.de>, lguest@ozlabs.org,
       jeremy@xensource.com, Steven Rostedt <srostedt@redhat.com>,
       Mike Travis <travis@sgi.com>
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Date: Thu, 13 Nov 2008 16:23:59 -0600
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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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