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

[xuehai zhang <hai@xxxxxxxxxxxxxxx>]

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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