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

To: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
Subject: Re: [Xen-devel] Xen 4.1 rc1 test report
From: Haitao Shan <maillists.shan@xxxxxxxxx>
Date: Wed, 26 Jan 2011 08:47:21 +0800
Cc: "Zheng, Shaohui" <shaohui.zheng@xxxxxxxxx>, Keir Fraser <keir@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
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I think it is basically the same idea as Keir introduced in 20841. I
guess this bug would happen on platforms which has large number of
physical CPUs, not only on EX system of Intel.
If you can cook the patch, that would be great! Thanks!!

Shan Haitao

2011/1/25 Ian Campbell <Ian.Campbell@xxxxxxxxxx>:
> 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?
> Ian.

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