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SubjectRe: ffsb create_4k 16% regression
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On Mon, 2009-06-29 at 16:06 +0800, Zhang, Yanmin wrote:
> I run many ffsb test cases on JBODs (typically 13/12 disks). Comparing
> with kernel 2.6.30, 2.6.31-rc1 has about 16% regression with
> ffsb_create_4k. The sub test case creates files continuously for 10
> minitues and every file is 1MB.
>
> Bisect located below patch.
>
>
> 5cee5815d1564bbbd505fea86f4550f1efdb5cd0 is first bad commit
> commit 5cee5815d1564bbbd505fea86f4550f1efdb5cd0
> Author: Jan Kara <jack@suse.cz>
> Date: Mon Apr 27 16:43:51 2009 +0200
>
> vfs: Make sys_sync() use fsync_super() (version 4)
>
> It is unnecessarily fragile to have two places (fsync_super() and do_sync())
> doing data integrity sync of the filesystem. Alter __fsync_super() to
> accommodate needs of both callers and use it. So after this patch
> __fsync_super() is the only place where we gather all the calls needed to
> properly send all data on a filesystem to disk.
>
>
> As a matter of fact, ffsb calls sys_sync in the end to make sure all data is
> flushed to disks and the flushing is counted into the result. vmstat shows
> ffsb is blocked when syncing for a long time. With 2.6.30, ffsb is blocked for
> a short time.
>
> I checked the patch and did experiments to recover the original methods. Eventually,
> the root cause is the patch deletes the calling to wakeup_pdflush when syncing, so
> only ffsb is blocked on disk I/O. wakeup_pdflush could ask pdflush to write back pages
> with ffsb at the same time.
>
> Below patch against 2.6.31-rc1 fixes it.
>
> Signed-off-by: Zhang Yanmin <yanmin_zhang@linux.intel.com>
>
> ---
>
> --- linux-2.6.31-rc1/fs/sync.c 2009-06-29 12:18:03.000000000 +0800
> +++ linux-2.6.31-rc1_sync/fs/sync.c 2009-06-29 14:56:49.000000000 +0800
> @@ -114,6 +114,7 @@ restart:
>
> SYSCALL_DEFINE0(sync)
> {
> + wakeup_pdflush(0);
> sync_filesystems(0);
> sync_filesystems(1);
> if (unlikely(laptop_mode))
Andrew,

Would you like to consider the patch for mm tree?

Thanks,
Yanmin


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