From: Jeff Moyer <jmoyer@redhat.com>
To: Vivek Goyal <vgoyal@redhat.com>
Cc: Christoph Hellwig <hch@infradead.org>,
Andrew Morton <akpm@linux-foundation.org>,
Shaohua Li <shaohua.li@intel.com>,
lkml <linux-kernel@vger.kernel.org>,
linux-mm <linux-mm@kvack.org>, Jens Axboe <axboe@kernel.dk>,
Herbert Poetzl <herbert@13thfloor.at>,
Eric Dumazet <eric.dumazet@gmail.com>,
Wu Fengguang <wfg@linux.intel.com>
Subject: Re: [PATCH] fix readahead pipeline break caused by block plug
Date: Wed, 01 Feb 2012 15:13:32 -0500 [thread overview]
Message-ID: <x49y5smpb0z.fsf@segfault.boston.devel.redhat.com> (raw)
In-Reply-To: <20120201201017.GC13246@redhat.com> (Vivek Goyal's message of "Wed, 1 Feb 2012 15:10:17 -0500")
Vivek Goyal <vgoyal@redhat.com> writes:
> On Wed, Feb 01, 2012 at 04:18:07AM -0500, Christoph Hellwig wrote:
>> On Tue, Jan 31, 2012 at 10:36:53PM -0500, Vivek Goyal wrote:
>> > I still see that IO is being submitted one page at a time. The only
>> > real difference seems to be that queue unplug happening at random times
>> > and many a times we are submitting much smaller requests (40 sectors, 48
>> > sectors etc).
>>
>> This is expected given that the block device node uses
>> block_read_full_page, and not mpage_readpage(s).
>
> What is the difference between block_read_full_page() and
> mpage_readpage(). IOW, why block device does not use mpage_readpage(s)
> interface?
>
> Is enabling mpage_readpages() on block devices is as simple as following
> patch or more is involved? (I suspect it has to be more than this. If it
> was this simple, it would have been done by now).
>
> This patch complies and seems to work. (system does not crash and dd
> seems to be working. I can't verify the contents of the file though).
>
> Applying following patch improved the speed from 110MB/s to more than
> 230MB/s.
>
> # dd if=/dev/sdb of=/dev/null bs=1M count=1K
> 1024+0 records in
> 1024+0 records out
> 1073741824 bytes (1.1 GB) copied, 4.6269 s, 232 MB/s
See:
commit db2dbb12dc47a50c7a4c5678f526014063e486f6
Author: Jeff Moyer <jmoyer@redhat.com>
Date: Wed Apr 22 14:08:13 2009 +0200
block: implement blkdev_readpages
Doing a proper block dev ->readpages() speeds up the crazy dump(8)
approach of using interleaved process IO.
Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
And:
commit 172124e220f1854acc99ee394671781b8b5e2120
Author: Jens Axboe <jens.axboe@oracle.com>
Date: Thu Jun 4 22:34:44 2009 +0200
Revert "block: implement blkdev_readpages"
This reverts commit db2dbb12dc47a50c7a4c5678f526014063e486f6.
It apparently causes problems with partition table read-ahead
on archs with large page sizes. Until that problem is diagnosed
further, just drop the readpages support on block devices.
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
;-)
Cheers,
Jeff
next prev parent reply other threads:[~2012-02-01 20:13 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-31 7:59 [PATCH] fix readahead pipeline break caused by block plug Shaohua Li
2012-01-31 8:36 ` Christoph Hellwig
2012-01-31 8:48 ` Eric Dumazet
2012-01-31 8:50 ` Herbert Poetzl
2012-01-31 8:53 ` Shaohua Li
2012-01-31 9:17 ` Eric Dumazet
2012-01-31 10:20 ` Wu Fengguang
2012-01-31 10:34 ` Wu Fengguang
2012-01-31 10:46 ` Christoph Hellwig
2012-01-31 10:57 ` Wu Fengguang
2012-01-31 11:34 ` Christoph Hellwig
2012-01-31 11:42 ` Wu Fengguang
2012-01-31 11:57 ` Christoph Hellwig
2012-01-31 12:20 ` Wu Fengguang
2012-02-01 2:25 ` Shaohua Li
2012-01-31 14:47 ` Vivek Goyal
2012-01-31 20:23 ` Vivek Goyal
2012-01-31 22:03 ` Vivek Goyal
2012-01-31 22:13 ` Andrew Morton
2012-01-31 22:22 ` Vivek Goyal
2012-02-01 3:36 ` Vivek Goyal
2012-02-01 7:10 ` Wu Fengguang
2012-02-01 16:01 ` Vivek Goyal
2012-02-01 9:18 ` Christoph Hellwig
2012-02-01 20:10 ` Vivek Goyal
2012-02-01 20:13 ` Jeff Moyer [this message]
2012-02-01 20:22 ` Andrew Morton
2012-02-01 7:02 ` Wu Fengguang
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