From: Andrew Morton <akpm@linux-foundation.org>
To: Vivek Goyal <vgoyal@redhat.com>
Cc: Christoph Hellwig <hch@infradead.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, 1 Feb 2012 12:22:41 -0800 [thread overview]
Message-ID: <20120201122241.db4056f6.akpm@linux-foundation.org> (raw)
In-Reply-To: <20120201201017.GC13246@redhat.com>
On Wed, 1 Feb 2012 15:10:17 -0500
Vivek Goyal <vgoyal@redhat.com> wrote:
> 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().
block_read_full_page() will attach buffer_heads to the page and will
perform IO via those buffer_heads. mpage_readpage() feeds the page
directly to the BIO layer and leaves it without attached buffer_heads.
> IOW, why block device does not use mpage_readpage(s)
> interface?
We've tried it in the past and problems ensued. A quick google search
for blkdev_readpages turns up stuff like
http://us.generation-nt.com/answer/patch-add-readpages-support-block-devices-help-201462802.html
> Applying following patch improved the speed from 110MB/s to more than
> 230MB/s.
Yeah. It should be doable - it would be a matter of hunting down and
squishing the oddball corner cases.
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next prev parent reply other threads:[~2012-02-01 20:22 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
2012-02-01 20:22 ` Andrew Morton [this message]
2012-02-01 7:02 ` Wu Fengguang
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