From: Linus Torvalds <torvalds@linux-foundation.org>
To: Jens Axboe <jens.axboe@oracle.com>
Cc: Arjan van de Ven <arjan@infradead.org>,
Theodore Tso <tytso@mit.edu>,
Linux Kernel Developers List <linux-kernel@vger.kernel.org>,
Ext4 Developers List <linux-ext4@vger.kernel.org>
Subject: Re: [GIT PULL] Ext3 latency fixes
Date: Mon, 6 Apr 2009 07:48:13 -0700 (PDT) [thread overview]
Message-ID: <alpine.LFD.2.00.0904060739570.4023@localhost.localdomain> (raw)
In-Reply-To: <20090406081616.GT5178@kernel.dk>
On Mon, 6 Apr 2009, Jens Axboe wrote:
>
> Well, either you are submitting a single piece of IO (in which case you
> just want to unplug or directly submit as part of the submit_bio()), or
> you are submitting several IOS (in which case you just want to unplug at
> the end of the IO submission, before waiting).
That's not true.
The plugging is often across multiple threads. It didn't _use_ to be (we
always unplugged at wait), but it is now. Nothing else explains why that
patch by Ted makes such a big throughput thing, because the code did
ret = submit_bh(WRITE_SYNC, bh);
wait_on_buffer(bh);
ie it very much submits a _single_ IO, and waits on it. If plugging made a
difference, that means that unplugging was delayed so long that somebody
else does IO too - ie it gets delayed past a wait event.
So according to your own rules, that submit_bh() _should_ use WRITE_SYNC,
but something bad happens if it does. I'm not quite seeing _what_, though,
unless there are multiple processes trying to dirty the _same_ buffer, and
they win if they all can dirty it without doing IO on it in between (and
then the write turns into just one write).
Linus
next prev parent reply other threads:[~2009-04-06 14:51 UTC|newest]
Thread overview: 69+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-04-03 7:01 [GIT PULL] Ext3 latency fixes Theodore Ts'o
2009-04-03 7:01 ` [PATCH 1/4] block_write_full_page: Use synchronous writes for WBC_SYNC_ALL writebacks Theodore Ts'o
2009-04-03 7:01 ` [PATCH 2/4] ext3: Use WRITE_SYNC for commits which are caused by fsync() Theodore Ts'o
2009-04-03 7:01 ` [PATCH 3/4] ext3: Add replace-on-truncate hueristics for data=writeback mode Theodore Ts'o
2009-04-03 7:01 ` [PATCH 4/4] ext3: Add replace-on-rename " Theodore Ts'o
2009-04-03 18:24 ` [GIT PULL] Ext3 latency fixes Linus Torvalds
2009-04-03 18:47 ` Jens Axboe
2009-04-03 19:13 ` Theodore Tso
2009-04-03 21:01 ` Chris Mason
2009-04-03 19:02 ` Linus Torvalds
2009-04-03 20:41 ` Linus Torvalds
2009-04-04 13:57 ` Theodore Tso
2009-04-04 15:16 ` Jens Axboe
2009-04-04 15:57 ` Linus Torvalds
2009-04-04 16:06 ` Linus Torvalds
2009-04-04 17:36 ` Jens Axboe
2009-04-04 17:34 ` Jens Axboe
2009-04-04 17:44 ` Linus Torvalds
2009-04-04 18:00 ` Trenton D. Adams
2009-04-04 18:01 ` Jens Axboe
2009-04-04 18:10 ` Linus Torvalds
2009-04-04 23:22 ` Theodore Tso
2009-04-04 23:33 ` Arjan van de Ven
2009-04-05 0:10 ` Theodore Tso
2009-04-05 15:05 ` Arjan van de Ven
2009-04-05 17:01 ` Linus Torvalds
2009-04-05 17:15 ` Mark Lord
2009-04-05 20:57 ` Jeff Garzik
2009-04-05 23:48 ` Arjan van de Ven
2009-04-06 2:32 ` Mark Lord
2009-04-06 5:47 ` Jeff Garzik
2009-04-07 18:18 ` Linus Torvalds
2009-04-07 18:22 ` Linus Torvalds
2009-04-07 19:40 ` [PATCH libata: add SSD detection hueristic; move SSD setup to ata_dev_configure (was Re: [GIT PULL] Ext3 latency fixes) Jeff Garzik
2009-04-09 18:21 ` Tejun Heo
2009-04-18 3:02 ` George Spelvin
2009-04-06 8:13 ` [GIT PULL] Ext3 latency fixes Jens Axboe
2009-04-05 18:56 ` Arjan van de Ven
2009-04-05 19:34 ` Linus Torvalds
2009-04-05 20:06 ` Arjan van de Ven
2009-04-06 6:25 ` Jens Axboe
2009-04-06 6:05 ` Theodore Tso
2009-04-06 6:23 ` Jens Axboe
2009-04-06 8:16 ` Jens Axboe
2009-04-06 14:48 ` Linus Torvalds [this message]
2009-04-06 15:09 ` Jens Axboe
2009-04-06 6:15 ` Jens Axboe
2009-04-04 20:18 ` Ingo Molnar
2009-04-06 21:50 ` Lennart Sorensen
2009-04-07 13:31 ` Mark Lord
2009-04-07 14:48 ` Lennart Sorensen
2009-04-07 19:21 ` Mark Lord
2009-04-07 19:57 ` Lennart Sorensen
2009-04-04 20:56 ` Arjan van de Ven
2009-04-06 7:06 ` Jens Axboe
2009-04-07 15:39 ` Indan Zupancic
2009-04-04 19:18 ` Theodore Tso
2009-04-06 8:12 ` Jens Axboe
2009-04-04 22:13 ` Linus Torvalds
2009-04-04 22:19 ` Linus Torvalds
2009-04-05 0:20 ` Theodore Tso
2009-04-03 19:54 ` Theodore Tso
2009-04-08 23:40 Theodore Ts'o
2009-04-09 15:49 ` Linus Torvalds
2009-04-09 16:23 ` Chris Mason
2009-04-09 17:49 ` Jan Kara
2009-04-09 18:10 ` Chris Mason
2009-04-09 19:04 ` Jan Kara
2009-04-09 17:36 ` Jan Kara
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