[lkml]   [2009]   [Jul]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [RESEND] [PATCH] readahead:add blk_run_backing_dev

Ronald Moesbergen, on 07/16/2009 11:32 AM wrote:
> 2009/7/15 Vladislav Bolkhovitin <>:
>>> The drop with 64 max_sectors_kb on the client is a consequence of how CFQ
>>> is working. I can't find the exact code responsible for this, but from all
>>> signs, CFQ stops delaying requests if amount of outstanding requests exceeds
>>> some threshold, which is 2 or 3. With 64 max_sectors_kb and 5 SCST I/O
>>> threads this threshold is exceeded, so CFQ doesn't recover order of
>>> requests, hence the performance drop. With default 512 max_sectors_kb and
>>> 128K RA the server sees at max 2 requests at time.
>>> Ronald, can you perform the same tests with 1 and 2 SCST I/O threads,
>>> please?
> Ok. Should I still use the file-on-xfs testcase for this, or should I
> go back to using a regular block device?

Yes, please

> The file-over-iscsi is quite
> uncommon I suppose, most people will export a block device over iscsi,
> not a file.

No, files are common. The main reason why people use direct block
devices is a not supported by anything believe that comparing with files
they "have less overhead", so "should be faster". But it isn't true and
can be easily checked.

>> With context-RA patch, please, in those and future tests, since it should
>> make RA for cooperative threads much better.
>>> You can limit amount of SCST I/O threads by num_threads parameter of
>>> scst_vdisk module.
> Ok, I'll try that and include the blk_run_backing_dev,
> readahead-context and io_context patches.
> Ronald.
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to
> More majordomo info at
> Please read the FAQ at

 \ /
  Last update: 2009-07-16 12:39    [W:0.222 / U:0.204 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site