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Re: [Xen-devel] open/stat64 syscalls run faster on Xen VM than standard

To: "Stephen C. Tweedie" <sct@xxxxxxxxxx>
Subject: Re: [Xen-devel] open/stat64 syscalls run faster on Xen VM than standard Linux
From: xuehai zhang <hai@xxxxxxxxxxxxxxx>
Date: Mon, 28 Nov 2005 10:27:54 -0600
Cc: "Petersson, Mats" <mats.petersson@xxxxxxx>, Tim Freeman <tfreeman@xxxxxxxxxxx>, Kate Keahey <keahey@xxxxxxxxxxx>, Xen Mailing List <xen-devel@xxxxxxxxxxxxxxxxxxx>
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Stephen,

Thanks for the reply.

I mounted the loopback file in dom0, chrooted to the mountpoint and redid the experiment. The results is attached below. The time of open and stat64 calls is similar to the XenLinux case and also much smaller than the standard Linux case. So, either using loopback file as backend of XenLinux or directly mounting it in local filesystem will result in some benefit (maybe just caused by the extra layer of block caching) for the performance of some system calls.


What time, exactly, is being measured here?  Is it wall-clock
gettimeofday? Or only elapsed time inside the domU?

The time is collected and reported by strace by using the gettimeofday function.

It would be
enlightening to re-measure the performance by counting the number of
times these operations can be completed in a second, just to get a
second opinion and to determine if the difference is genuine or if it's
just an artifact of how we're measuring time when multiple domains are
involved.

Your questioning makes sense to me. But I am not very sure about how to effectively count how many these operations can be completed in a second. Can you give me some hint?

Thanks again.

Xuehai


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