On Tue, Jul 12, 2011 at 06:43:51PM +0800, Tao Ma wrote: > From: Tao Ma <boyu.mt@xxxxxxxxxx> > > In commit 749ef9f8423, we use WRITE_SYNC instead of WRITE in > journal_commit_transaction. It causes a much heavy burden for > the disk as now the seqenctial write can't be merged(see the blktrace below). Tao Ma, Few queries. - What's the workload you are using for this test. - Do you see any performance improvement by switching to WRITE_SYNC_PLUG. - Why writes are not being merged? Because request got dispatched immediately? Do you have logs for insertion of requests also. - WRITE_SYNC_PLUG will plug the queue and expects explicity unplug. Who is doing unplug in this case? - I am not sure in how many cases we are expecting to submit multiple sequential write here. Thanks Vivek > > Given the description of that commit 749ef9f8423, the reason why > we use WRITE_SYNC is that it wants to use REQ_NOIDLE and WRITE_SYNC_PLUG > also has that flag, so use WRITE_SYNC_PLUG instead. From blktrace, > we can get that: > > without the patch: > 8,0 6 18 0.016058423 3342 D W 461101317 + 4 [jbd2/sda11-8] > 8,0 6 19 0.016065473 3342 D W 461101321 + 4 [jbd2/sda11-8] > 8,0 6 20 0.016070751 3342 D W 461101325 + 4 [jbd2/sda11-8] > 8,0 6 21 0.016076180 3342 D W 461101329 + 4 [jbd2/sda11-8] > 8,0 6 22 0.016081255 3342 D W 461101333 + 4 [jbd2/sda11-8] > 8,0 6 23 0.016085963 3342 D W 461101337 + 4 [jbd2/sda11-8] > 8,0 6 24 0.016182048 0 C W 461101317 + 4 [0] > 8,0 6 25 0.016190820 0 C W 461101325 + 4 [0] > 8,0 6 26 0.016193927 0 C W 461101321 + 4 [0] > 8,0 6 27 0.016196532 0 C W 461101333 + 4 [0] > 8,0 6 28 0.016199180 0 C W 461101337 + 4 [0] > 8,0 6 29 0.016206180 0 C W 461101329 + 4 [0] > > with this patch: > 8,0 4 23 4.320315739 3129 D W 461101317 + 24 [jbd2/sda11-8] > 8,0 4 24 4.320364518 0 C W 461101317 + 24 [0] > > This only affects .37 and .38 since Jens' new plug patches are included > in .39 and the bug is removed as a side effect. But I think it is needed > anyway for the stable. And RHEL6 needs this also I guess. > > Cc: stable@xxxxxxxxxx # 2.6.37 and 2.6.38 > Cc: Jan Kara <jack@xxxxxxx> > Cc: Vivek Goyal <vgoyal@xxxxxxxxxx> > Cc: Jeff Moyer <jmoyer@xxxxxxxxxx> > Cc: Corrado Zoccolo <czoccolo@xxxxxxxxx> > Cc: Jens Axboe <jaxboe@xxxxxxxxxxxx> > Signed-off-by: Tao Ma <boyu.mt@xxxxxxxxxx> > --- > fs/jbd/commit.c | 9 +-------- > fs/jbd2/commit.c | 9 +-------- > 2 files changed, 2 insertions(+), 16 deletions(-) > > diff --git a/fs/jbd/commit.c b/fs/jbd/commit.c > index 34a4861..6d13df5 100644 > --- a/fs/jbd/commit.c > +++ b/fs/jbd/commit.c > @@ -294,7 +294,7 @@ void journal_commit_transaction(journal_t *journal) > int first_tag = 0; > int tag_flag; > int i; > - int write_op = WRITE_SYNC; > + int write_op = WRITE_SYNC_PLUG; > > /* > * First job: lock down the current transaction and wait for > @@ -327,13 +327,6 @@ void journal_commit_transaction(journal_t *journal) > spin_lock(&journal->j_state_lock); > commit_transaction->t_state = T_LOCKED; > > - /* > - * Use plugged writes here, since we want to submit several before > - * we unplug the device. We don't do explicit unplugging in here, > - * instead we rely on sync_buffer() doing the unplug for us. > - */ > - if (commit_transaction->t_synchronous_commit) > - write_op = WRITE_SYNC_PLUG; > spin_lock(&commit_transaction->t_handle_lock); > while (commit_transaction->t_updates) { > DEFINE_WAIT(wait); > diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c > index f3ad159..fc3840f 100644 > --- a/fs/jbd2/commit.c > +++ b/fs/jbd2/commit.c > @@ -329,7 +329,7 @@ void jbd2_journal_commit_transaction(journal_t *journal) > int tag_bytes = journal_tag_bytes(journal); > struct buffer_head *cbh = NULL; /* For transactional checksums */ > __u32 crc32_sum = ~0; > - int write_op = WRITE_SYNC; > + int write_op = WRITE_SYNC_PLUG; > > /* > * First job: lock down the current transaction and wait for > @@ -363,13 +363,6 @@ void jbd2_journal_commit_transaction(journal_t *journal) > write_lock(&journal->j_state_lock); > commit_transaction->t_state = T_LOCKED; > > - /* > - * Use plugged writes here, since we want to submit several before > - * we unplug the device. We don't do explicit unplugging in here, > - * instead we rely on sync_buffer() doing the unplug for us. > - */ > - if (commit_transaction->t_synchronous_commit) > - write_op = WRITE_SYNC_PLUG; > trace_jbd2_commit_locking(journal, commit_transaction); > stats.run.rs_wait = commit_transaction->t_max_wait; > stats.run.rs_locked = jiffies; > -- > 1.7.4 -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html