On Tue, Nov 06, 2007 at 10:53:25PM +0100, Torsten Kaiser wrote:
> On 11/6/07, David Chinner <[email protected]> wrote:
> > Rather than vmstat, can you use something like iostat to show how busy your
> > disks are? i.e. are we seeing RMW cycles in the raid5 or some such issue.
>
> Both "vmstat 10" and "iostat -x 10" output from this test:
> procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
> r b swpd free buff cache si so bi bo in cs us sy id wa
> 2 0 0 3700592 0 85424 0 0 31 83 108 244 2 1 95 1
> -> emerge reads something, don't knwo for sure what...
> 1 0 0 3665352 0 87940 0 0 239 2 343 585 2 1 97 0
....
>
> The last 20% of the btrace look more or less completely like this, no
> other programs do any IO...
>
> 253,0 3 104626 526.293450729 974 C WS 79344288 + 8 [0]
> 253,0 3 104627 526.293455078 974 C WS 79344296 + 8 [0]
> 253,0 1 36469 444.513863133 1068 Q WS 154998480 + 8 [xfssyncd]
> 253,0 1 36470 444.513863135 1068 Q WS 154998488 + 8 [xfssyncd]
^^
Apparently we are doing synchronous writes. That would explain why
it is slow. We shouldn't be doing synchronous writes here. I'll see if
I can reproduce this.
<goes off and looks>
Yes, I can reproduce the sync writes coming out of xfssyncd. I'll
look into this further and send a patch when I have something concrete.
Cheers,
Dave.
--
Dave Chinner
Principal Engineer
SGI Australian Software Group
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