From mboxrd@z Thu Jan  1 00:00:00 1970
From: xuehai zhang <hai@cs.uchicago.edu>
Subject: Re: open/stat64 syscalls run faster on Xen VM
	than	standard Linux
Date: Mon, 28 Nov 2005 10:27:54 -0600
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To: "Stephen C. Tweedie" <sct@redhat.com>
Cc: "Petersson, Mats" <mats.petersson@amd.com>, Tim Freeman <tfreeman@mcs.anl.gov>, Kate Keahey <keahey@mcs.anl.gov>, Xen Mailing List <xen-devel@lists.xensource.com>
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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