Re: [RESEND] [PATCH] readahead:add blk_run_backing_dev

[Ronald Moesbergen <intercommit@gmail.com>]

2009/6/29 Wu Fengguang <fengguang.wu@intel.com>:
> On Mon, Jun 29, 2009 at 09:13:27PM +0800, Wu Fengguang wrote:
>> On Mon, Jun 29, 2009 at 09:04:57PM +0800, Vladislav Bolkhovitin wrote:
>> > Wu Fengguang, on 06/29/2009 04:54 PM wrote:
>> > >
>> > > Why not 2.6.30? :)
>> >
>> > We started with 2.6.29, so why not complete with it (to save additional
>> > Ronald's effort to move on 2.6.30)?
>>
>> OK, that's fair enough.
>
> btw, I backported the 2.6.31 context readahead patches to 2.6.29, just
> in case it will help the SCST performance.
>
> Ronald, if you run context readahead, please make sure that the server
> side readahead size is bigger than the client side readahead size.

I tried this patch on a vanilla kernel and no other patches applied,
but it does not seem to help. The iSCSI throughput does not go above
60MB/s. (1GB in 17 seconds). I have tried several readahead settings
from 128KB up to 4MB and kept the server readahead at twice the client
readahead, but it never comes above 60MB/s. This is using SCST on the
serverside and openiscsi on the client. I get much better throughput
(90 MB/s) when using the patches supplied with SCST, together with the
blk_run_backing_dev readahead patch.

Ronald.