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Re: [Xen-devel] Latency spike during page_scrub_softirq

To: Chris Lalancette <clalance@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] Latency spike during page_scrub_softirq
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Thu, 02 Jul 2009 16:13:09 +0100
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On 02/07/2009 15:47, "Chris Lalancette" <clalance@xxxxxxxxxx> wrote:

> There are a couple of solutions that I can think of:
> 1)  Just clear the pages inside free_domheap_pages().  I tried this with a
> 64GB
> guest as mentioned above, and I didn't see any ill effects from doing so.  It
> seems like this might actually be a valid way to go, although then a single
> is doing all of the work of freeing the pages (might be a problem on UP
> systems).

Now that domain destruction is preemptible all the way back up to libxc, I
think the page-scrub queue is not so much required. And it seems it never
worked very well anyway! I will remove it.

This may make 'xm destroy' operations take a while, but actually this may be
more sensibly handled by punting the destroy hypercall into another thread
at dom0 userspace level, rather than doing the shonky 'scheduling' we
attempt in Xen itself right now.

 -- Keir

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