From: Zhang, Yanmin Date: Sun, 5 Jul 2009 19:08:08 +0000 (-0700) Subject: sys_sync(): fix 16% performance regression in ffsb create_4k test X-Git-Url: http://git.cdn.openwrt.org/?a=commitdiff_plain;h=3beab0b42413e83a7907db7176b54c840fc75a81;p=openwrt%2Fstaging%2Fblogic.git sys_sync(): fix 16% performance regression in ffsb create_4k test 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 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. [akpm@linux-foundation.org: restore comment too] Signed-off-by: Zhang Yanmin Cc: Jan Kara Cc: Al Viro Acked-by: Jens Axboe Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/fs/sync.c b/fs/sync.c index dd200025af85..3422ba61d86d 100644 --- a/fs/sync.c +++ b/fs/sync.c @@ -112,8 +112,13 @@ restart: mutex_unlock(&mutex); } +/* + * sync everything. Start out by waking pdflush, because that writes back + * all queues in parallel. + */ SYSCALL_DEFINE0(sync) { + wakeup_pdflush(0); sync_filesystems(0); sync_filesystems(1); if (unlikely(laptop_mode))