From: Wu Fengguang <wfg@linux.intel.com>
To: Shaohua Li <shaohua.li@intel.com>
Cc: Herbert Poetzl <herbert@13thfloor.at>,
Eric Dumazet <eric.dumazet@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
LKML <linux-kernel@vger.kernel.org>, Jens Axboe <axboe@kernel.dk>,
Tejun Heo <tj@kernel.org>
Subject: Re: Bad SSD performance with recent kernels
Date: Mon, 30 Jan 2012 22:28:37 +0800 [thread overview]
Message-ID: <20120130142837.GA21750@localhost> (raw)
In-Reply-To: <CANejiEXwt7zdWRD0gTg1JXNPZ52vU1Z4cQsb3xztqDLccyTPSQ@mail.gmail.com>
On Mon, Jan 30, 2012 at 06:31:34PM +0800, Li, Shaohua wrote:
> Looks the 2.6.39 block plug introduces some latency here. deleting
> blk_start_plug/blk_finish_plug in generic_file_aio_read seems
> workaround
> the issue. The plug seems not good for sequential IO, because readahead
> code already has plug and has fine grained control.
Why not remove the generic_file_aio_read() plug completely? It
actually prevents unplugging immediately after the readahead IO is
submitted and in turn stalls the IO pipeline as showed by Eric's
blktrace data.
Eric, will you test this patch? Thank you.
--- linux.orig/mm/filemap.c 2012-01-30 22:27:11.000000000 +0800
+++ linux/mm/filemap.c 2012-01-30 22:27:25.000000000 +0800
@@ -1414,15 +1414,12 @@ generic_file_aio_read(struct kiocb *iocb
unsigned long seg = 0;
size_t count;
loff_t *ppos = &iocb->ki_pos;
- struct blk_plug plug;
count = 0;
retval = generic_segment_checks(iov, &nr_segs, &count, VERIFY_WRITE);
if (retval)
return retval;
- blk_start_plug(&plug);
-
/* coalesce the iovecs and go direct-to-BIO for O_DIRECT */
if (filp->f_flags & O_DIRECT) {
loff_t size;
@@ -1495,7 +1492,6 @@ generic_file_aio_read(struct kiocb *iocb
break;
}
out:
- blk_finish_plug(&plug);
return retval;
}
EXPORT_SYMBOL(generic_file_aio_read);
next prev parent reply other threads:[~2012-01-30 14:38 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-27 6:00 Bad SSD performance with recent kernels Herbert Poetzl
2012-01-27 6:44 ` Eric Dumazet
2012-01-28 12:51 ` Wu Fengguang
2012-01-28 13:33 ` Eric Dumazet
2012-01-29 5:59 ` Wu Fengguang
2012-01-29 8:42 ` Herbert Poetzl
2012-01-29 9:28 ` Wu Fengguang
2012-01-29 10:03 ` Eric Dumazet
2012-01-29 11:16 ` Wu Fengguang
2012-01-29 13:13 ` Eric Dumazet
2012-01-29 15:52 ` Pádraig Brady
2012-01-29 16:10 ` Wu Fengguang
2012-01-29 20:15 ` Herbert Poetzl
2012-01-30 11:18 ` Wu Fengguang
2012-01-30 12:34 ` Eric Dumazet
2012-01-30 14:01 ` Wu Fengguang
2012-01-30 14:05 ` Wu Fengguang
2012-01-30 3:17 ` Shaohua Li
2012-01-30 5:31 ` Eric Dumazet
2012-01-30 5:45 ` Shaohua Li
2012-01-30 7:13 ` Herbert Poetzl
2012-01-30 7:22 ` Shaohua Li
2012-01-30 7:36 ` Herbert Poetzl
2012-01-30 8:12 ` Shaohua Li
2012-01-30 10:31 ` Shaohua Li
2012-01-30 14:28 ` Wu Fengguang [this message]
2012-01-30 14:51 ` Eric Dumazet
2012-01-30 22:26 ` Vivek Goyal
2012-01-31 0:14 ` Shaohua Li
2012-01-31 1:07 ` Wu Fengguang
2012-01-31 3:00 ` Shaohua Li
2012-01-31 2:17 ` Eric Dumazet
2012-01-31 8:46 ` Eric Dumazet
2012-01-31 6:36 ` Herbert Poetzl
2012-01-30 14:48 ` Wu Fengguang
2012-01-28 17:01 ` Herbert Poetzl
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