From: Andrew Morton <akpm@linux-foundation.org>
To: Christoph Hellwig <hch@infradead.org>
Cc: Dan Ehrenberg <dehrenberg@google.com>,
Alexander Viro <viro@zeniv.linux.org.uk>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] dio: Fast-path for page-aligned IOs
Date: Wed, 27 Jul 2011 14:14:15 -0700 [thread overview]
Message-ID: <20110727141415.a67cafb8.akpm@linux-foundation.org> (raw)
In-Reply-To: <20110727210828.GB12714@infradead.org>
On Wed, 27 Jul 2011 17:08:28 -0400
Christoph Hellwig <hch@infradead.org> wrote:
> On Mon, Jun 20, 2011 at 04:17:35PM -0700, Dan Ehrenberg wrote:
> > The fast path does not apply for operations of the wrong size
> > or alignmnent, or for operations on raw drives with 512-byte sectors.
> > It might be possible to make this special case a little more general
> > while maintaining its performance benefits, but I do not believe that
> > the full performance benefits can be achieved without resorting to
> > special handling of simple cases, as is done in this patch.
>
> Did you check how this compares to Andis small optimizations?
>
> Also operations on raw disks are something people with fast devices
> care about a lot. We often hear about benchmark regressions due to
> stupid little things in the direct I/O code.
>
> If we want to special case something that would be a very easy target,
> with a 1:1 mapping of logical to physical blocks and thus no need
> to call the allocator first, and no need for any kind of locking
> or alignment handling.
Ken did this back in 2006
(http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=e61c90188b9956edae1105eef361d8981a352fcd)
but we reverted that shortly afterwards for some reason.
next prev parent reply other threads:[~2011-07-27 21:14 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-06-20 23:17 Dan Ehrenberg
2011-06-21 20:41 ` Andi Kleen
2011-06-21 21:21 ` Daniel Ehrenberg
2011-06-21 21:44 ` Andi Kleen
2011-07-27 21:08 ` Christoph Hellwig
2011-07-27 21:14 ` Andrew Morton [this message]
2011-07-27 22:15 ` Jeff Moyer
2011-07-28 22:09 ` Daniel Ehrenberg
2011-07-28 22:10 ` Daniel Ehrenberg
-- strict thread matches above, loose matches on Subject: below --
2011-06-20 22:44 Dan Ehrenberg
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