2008-01-22 15:25:19

by Martin Knoblauch

[permalink] [raw]
Subject: Re: regression: 100% io-wait with 2.6.24-rcX


------------------------------------------------------
Martin Knoblauch
email: k n o b i AT knobisoft DOT de
www: http://www.knobisoft.de

----- Original Message ----
> From: Alasdair G Kergon <[email protected]>
> To: Martin Knoblauch <[email protected]>
> Cc: Linus Torvalds <[email protected]>; Mel Gorman <[email protected]>; Fengguang Wu <[email protected]>; Mike Snitzer <[email protected]>; Peter Zijlstra <[email protected]>; [email protected]; Ingo Molnar <[email protected]>; [email protected]; "[email protected]" <[email protected]>; [email protected]; Jens Axboe <[email protected]>; Milan Broz <[email protected]>; Neil Brown <[email protected]>
> Sent: Tuesday, January 22, 2008 3:39:33 PM
> Subject: Re: regression: 100% io-wait with 2.6.24-rcX
>
> On Fri, Jan 18, 2008 at 11:01:11AM -0800, Martin Knoblauch wrote:
> > At least, rc1-rc5 have shown that the CCISS system can do well. Now
> > the question is which part of the system does not cope well with the
> > larger IO sizes? Is it the CCISS controller, LVM or both. I am
> open
>
to
> > suggestions on how to debug that.
>
> What is your LVM device configuration?
> E.g. 'dmsetup table' and 'dmsetup info -c' output.
> Some configurations lead to large IOs getting split up on the
> way
>
through
> device-mapper.
>
Hi Alastair,

here is the output, the filesystem in question is on LogVol02:

[[email protected] ~]# dmsetup table
VolGroup00-LogVol02: 0 350945280 linear 104:2 67109248
VolGroup00-LogVol01: 0 8388608 linear 104:2 418054528
VolGroup00-LogVol00: 0 67108864 linear 104:2 384
[[email protected] ~]# dmsetup info -c
Name Maj Min Stat Open Targ Event UUID
VolGroup00-LogVol02 253 1 L--w 1 1 0 LVM-IV4PeE8cdxA3piC1qk79GY9PE9OC4OgmOZ4OzOgGQIdF3qDx6fJmlZukXXLIy39R
VolGroup00-LogVol01 253 2 L--w 1 1 0 LVM-IV4PeE8cdxA3piC1qk79GY9PE9OC4Ogmfn2CcAd2Fh7i48twe8PZc2XK5bSOe1Fq
VolGroup00-LogVol00 253 0 L--w 1 1 0 LVM-IV4PeE8cdxA3piC1qk79GY9PE9OC4OgmfYjxQKFP3zw2fGsezJN7ypSrfmP7oSvE

> See if these patches make any difference:
>
http://www.kernel.org/pub/linux/kernel/people/agk/patches/2.6/editing/
>
> dm-md-merge_bvec_fn-with-separate-bdev-and-sector.patch
> dm-introduce-merge_bvec_fn.patch
> dm-linear-add-merge.patch
> dm-table-remove-merge_bvec-sector-restriction.patch
>

thanks for the suggestion. Are they supposed to apply to mainline?

Cheers
Martin


2008-01-22 23:42:09

by Alasdair G Kergon

[permalink] [raw]
Subject: Re: regression: 100% io-wait with 2.6.24-rcX

On Tue, Jan 22, 2008 at 07:25:15AM -0800, Martin Knoblauch wrote:
> [[email protected] ~]# dmsetup table
> VolGroup00-LogVol02: 0 350945280 linear 104:2 67109248
> VolGroup00-LogVol01: 0 8388608 linear 104:2 418054528
> VolGroup00-LogVol00: 0 67108864 linear 104:2 384

The IO should pass straight through simple linear targets like that without
needing to get broken up, so I wouldn't expect those patches to make any
difference in this particular case.

Alasdair
--
[email protected]