Re: open/stat64 syscalls run faster on Xen VM than standard Linux

[xuehai zhang <hai@cs.uchicago.edu>]

Mats,

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.

# strace -c /bin/sh -c /bin/echo foo

% time     seconds  usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
  21.93    0.000490         490         1           write
  16.34    0.000365          24        15           old_mmap
  15.26    0.000341          38         9         3 open
   9.62    0.000215          43         5           read
   7.97    0.000178          10        18           brk
   7.79    0.000174          87         2           munmap
   4.07    0.000091           8        11           rt_sigaction
   3.27    0.000073          12         6           close
   2.91    0.000065          11         6           fstat64
   2.28    0.000051           9         6           rt_sigprocmask
   2.15    0.000048          24         2           access
   1.75    0.000039          13         3           uname
   1.66    0.000037          19         2           stat64
   0.40    0.000009           9         1           getpgrp
   0.40    0.000009           9         1           getuid32
   0.36    0.000008           8         1           time
   0.36    0.000008           8         1           getppid
   0.36    0.000008           8         1           getgid32
   0.31    0.000007           7         1           getpid
   0.27    0.000006           6         1           execve
   0.27    0.000006           6         1           geteuid32
   0.27    0.000006           6         1           getegid32
------ ----------- ----------- --------- --------- ----------------
100.00    0.002234                    95         3 total

Thanks.

Xuehai


Petersson, Mats wrote:
>>-----Original Message-----
>>From: xen-devel-bounces@lists.xensource.com 
>>[mailto:xen-devel-bounces@lists.xensource.com] On Behalf Of 
>>Anthony Liguori
>>Sent: 28 November 2005 14:39
>>To: xuehai zhang
>>Cc: Xen Mailing List
>>Subject: Re: [Xen-devel] open/stat64 syscalls run faster on 
>>Xen VM than standard Linux
>>
>>This may just be the difference between having the extra 
>>level of block caching from using a loop back device.
>>
>>Try running the same benchmark on a domain that uses an 
>>actual partition.  While the syscalls may appear to be 
>>faster, I imagine it's because the cost of pulling in a block 
>>has already been payed so the overall workload is unaffected.
> 
> 
> And this would be the same as running standard linux with the loopback
> file-system mounted and chroot to the local file-system, or would that
> be different? [I'm asking because I don't actually understand enough
> about how it works to know what difference it makes, and I would like to
> know, because at some point I'll probably need to know this.]
> 
> --
> Mats
> 
>>Regards,
>>
>>Anthony Liguori
>>
>>xuehai zhang wrote:
> 
> [snip]
> 
>