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.5cee5815d1
is first bad commit commit5cee5815d1
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. [akpm@linux-foundation.org: restore comment too] Signed-off-by: Zhang Yanmin <yanmin_zhang@linux.intel.com> Cc: Jan Kara <jack@suse.cz> Cc: Al Viro <viro@zeniv.linux.org.uk> Acked-by: Jens Axboe <jens.axboe@oracle.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -112,8 +112,13 @@ static void sync_filesystems(int wait)
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mutex_unlock(&mutex);
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}
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/*
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* sync everything. Start out by waking pdflush, because that writes back
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* all queues in parallel.
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*/
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SYSCALL_DEFINE0(sync)
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{
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wakeup_pdflush(0);
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sync_filesystems(0);
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sync_filesystems(1);
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if (unlikely(laptop_mode))
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