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Re: [Xen-devel] Xen 4.1 rc1 test report

To: Haitao Shan <maillists.shan@xxxxxxxxx>
Subject: Re: [Xen-devel] Xen 4.1 rc1 test report
From: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
Date: Tue, 25 Jan 2011 11:43:18 +0000
Cc: "Zheng, Shaohui" <shaohui.zheng@xxxxxxxxx>, Keir Fraser <keir@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
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On Tue, 2011-01-25 at 06:24 +0000, Haitao Shan wrote:
> > Performance(1 bug)
> > 1. guest boot very slowly without limit dom0 cpu number on EX (Intel)
> > http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=1719
> >
> This bug happened 1 year before. Keir has made a fix with c/s 20841,
> which essentially holds the locked (and hence allocated) hypercall
> page so that next hypercall can reuse it without doing alloc and mlock
> again. By doing this, overhead of rschedule IPI as a result of
> frequent mlock is greatly reduced.
> Late in year 2010, libxc introduced a new mechanism called hypercall
> buffers, as you can refer c/s 22288~22312. Keir's fix is dropped in
> this new framework. As a result, the bug appears again.
> Probably the new framework auther can pick up Keir's fix again?

I think it would make sense to include a low water mark of a small
number of pages (perhaps 4 or 8) which instead of being freed are kept
and reused in preference to future new allocations. These pages would
only finally be released by the xc_interface_close() call.

Is this something which you feel able to make a patch for?


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