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Re: [Xen-devel] million cycle interrupt

To: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>, "Xen-Devel (E-mail)" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] million cycle interrupt
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Mon, 13 Apr 2009 09:23:58 +0100
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On 12/04/2009 21:16, "Dan Magenheimer" <dan.magenheimer@xxxxxxxxxx> wrote:

> Is a million cycles in an interrupt handler bad?  Any idea what
> might be consuming this?  The evidence might imply more cpus
> means longer interrupt, which bodes poorly for larger machines.
> I tried disabling the timer rendezvous code (not positive I
> was successful), but still got large measurements, and
> eventually the machine froze up (but not before I observed
> the stime skew climbing quickly to the millisecond-plus
> range).

You can instrument irq_enter() and irq_exit() to read TSC and find out the
distribution of irq handling times for interruptions that Xen knows about.
Otherwise who knows, it could even be system management mode on that
particular box.

 -- Keir

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