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SubjectRe: [PATCH 0/3 v5][RFC] ext3/4: enhance fsync performance when using CFQ
On Tue, Jun 22, 2010 at 05:34:59PM -0400, Jeff Moyer wrote:
> Hi,
>
> Running iozone with the fsync flag, or fs_mark, the performance of CFQ is
> far worse than that of deadline for enterprise class storage when dealing
> with file sizes of 8MB or less. I used the following command line as a
> representative test case:
>
> fs_mark -S 1 -D 10000 -N 100000 -d /mnt/test/fs_mark -s 65536 -t 1 -w 4096 -F
>
> When run using the deadline I/O scheduler, an average of the first 5 numbers
> will give you 448.4 files / second. CFQ will yield only 106.7. With
> this patch series applied (and the two patches I sent yesterday), CFQ now
> achieves 462.5 files / second.
>
> This patch set is still an RFC. I'd like to make it perform better when
> there is a competing sequential reader present. For now, I've addressed
> the concerns voiced about the previous posting.

What happened to the initial idea of just using the BIO_RW_META flag
for log writes? In the end log writes are the most important writes you
have in a journaled filesystem, and they should not be effect to any
kind of queue idling logic or other interruption. Log I/O is usually
very little (unless you use old XFS code with a worst-case directory
manipulation workload), and very latency sensitive.


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