Re: IO on guest is 20 times slower than host

From: "Kurt Yoder" <ktykvm@yoderhome.com>
To: "Avi Kivity" <avi@redhat.com>
Cc: kvm@vger.kernel.org
Subject: Re: IO on guest is 20 times slower than host
Date: Fri, 27 Mar 2009 10:03:47 -0400 (EDT)	[thread overview]
Message-ID: <52849.140.147.222.3.1238162627.squirrel@dyn.yoderhome.com> (raw)
In-Reply-To: <52808.140.147.222.3.1238162037.squirrel@dyn.yoderhome.com>

>> Kurt Yoder wrote:

<snip>

> me@guest:~# vmstat 1
> procs -----------memory---------- ---swap-- -----io---- -system--
> ----cpu----
>  r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id
> wa
>  1  0   2616 686488   7756 208004    0    0     2    34   10    3  0  1 99
>  0
>  1  0   2616 680280   7764 213920    0    0     0     0  106    8  7 93  0
>  0
>  1  0   2616 674076   7768 219768    0    0     0     0  104    5  8 92  0
>  0
>  1  0   2616 669000   7780 224864    0    0     0 15124  188   14  1 99  0
>  0
>  1  0   2616 663168   7788 230700    0    0     0     0  104    5  4 96  0
>  0
>  1  0   2616 657836   7792 235472    0    0     0  5684  139   21  5 95  0
>  0
>  1  0   2616 651648   7796 241288    0    0     0     0  104    5  7 93  0
>  0
>  1  0   2616 645428   7804 247136    0    0     0     0  104    5  2 98  0
>  0
>  1  0   2616 640956   7816 251908    0    0     0 22164  232   31  3 97  0
>  0
>  1  0   2616 635016   7820 257732    0    0     0     0  104    5  2 98  0
>  0
>  1  0   2616 629204   7828 263552    0    0     0     0  105    9  2 98  0
>  0
>  1  0   2616 622732   7832 269392    0    0     0     0  104    5  5 95  0
>  0
>  1  0   2616 616676   7840 275096    0    0     0     0  104    7  5 95  0
>  0
>  1  0   2616 612200   7852 279540    0    0     0 27872  263   39  1 99  0
>  0
>  1  0   2616 606384   7856 285204    0    0     0     0  105    7  3 97  0
>  0
>  1  0   2616 600536   7860 290716    0    0     0     0  104   11  7 93  0
>  0
>  1  0   2616 594352   7868 296408    0    0     0     0  104    7  9 91  0
>  0

BTW, for comparison I did the same test on the other KVM host/guest, and
here is the vmstat -1:

me@otherhost:/etc/apache2# vmstat 1
procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa
 3  0  55636   4520    956  37504    0    0    12    12   26   19  0  0 99  0
 3  0  55636   3332    620  38516    0    0     0 81880  537  355  4 92  0  4
 2  1  55636   3232    684  38508    0    0     8 56660 1708  550  2 97  0  1
 2  1  55636   3200    764  38440    0    0     0 87696  409  271  4 96  0  0
 2  1  55636   3096    852  38532    0    0     4 82824  394  254  4 95  0  1
 3  1  55636   3072    848  38776    0    0    12 83520  429  293  8 91  0  1
 3  1  55636   3204    536  38644    0    0    12 64856 1313  464  4 94  0  2
 3  1  55636   3088    620  38484  192    0   280 85632  467  314  5 94  0  1
 2  1  55636   3180    684  38428    0    0     0 67368 1011  443  3 97  0  0
 2  1  55636   3080    768  38456  148    0   220 81432  414  270  8 91  0  1
 3  0  55636   3124    784  38952    0    0    16 80416  554  284  5 94  0  1
 3  1  55636   3004    488  38968    0    0     4 57756 1195  439  4 96  0  0
 1  0  55636   4208    556  37644    0    0     4 75680  545  336  6 92  0  2
 1  1  55636   3296    644  38388    0    0     0 87024  299  339  3 97  0  0
 2  1  55636   2992    724  38648    0    0     4 78792  293  341  4 92  0  4
 3  1  55636   3164    804  38660    0    0     8 73648  462  369  4 83  0 13
 2  0  55636   2988    492  39044    0    0     8 73168  492  424  3 86  0 11

So clearly there is something odd going on with the first one. It looks
like it's CPU-bound, and this is throttling the IO?

-Kurt