linux-ext4 - Re: [PATCH v5.2 00/14] crc32c: Add faster algorithm and self-test code

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Message-ID: <20111201202053.GG1495@noexit.corp.google.com>
Date:	Thu, 1 Dec 2011 12:20:53 -0800
From:	Joel Becker <jlbec@...lplan.org>
To:	"Darrick J. Wong" <djwong@...ibm.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Theodore Tso <tytso@....edu>,
	Joakim Tjernlund <joakim.tjernlund@...nsmode.se>,
	Bob Pearson <rpearson@...temfabricworks.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	linux-crypto <linux-crypto@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Mingming Cao <cmm@...ibm.com>, linux-ext4@...r.kernel.org,
	Herbert Xu <herbert@...dor.apana.org.au>
Subject: Re: [PATCH v5.2 00/14] crc32c: Add faster algorithm and self-test
 code

On Thu, Dec 01, 2011 at 12:13:41PM -0800, Darrick J. Wong wrote:
> Hi all,
> 
> This patchset (re)uses Bob Pearson's crc32 slice-by-8 code to stamp out a
> software crc32c implementation.  It removes the crc32c implementation in
> crypto/ in favor of using the stamped-out one in lib/.  There is also a change
> to Kconfig so that the kernel builder can pick an implementation best suited
> for the hardware.
> 
> The motivation for this patchset is that I am working on adding full metadata
> checksumming to ext4.  As far as performance impact of adding checksumming
> goes, I see nearly no change with a standard mail server ffsb simulation.  On a
> test that involves only file creation and deletion and extent tree writes, I
> see a drop of about 50 pcercent with the current kernel crc32c implementation;
> this improves to a drop of about 20 percent with the enclosed crc32c code.
> 
> When metadata is usually a small fraction of total IO, this new implementation
> doesn't help much because metadata is usually a small fraction of total IO.
> However, when we are doing IO that is almost all metadata (such as rm -rf'ing a
> tree), then this patch speeds up the operation substantially.
> 
> Incidentally, given that iscsi, sctp, and btrfs also use crc32c, this patchset
> should improve their speed as well.  I have not yet quantified that, however.

	I thought they usually used the SSE instruction for crc32 or
equivalent.

Joel

-- 

"I almost ran over an angel
 He had a nice big fat cigar.
 'In a sense,' he said, 'You're alone here
 So if you jump, you'd best jump far.'"

			http://www.jlbec.org/
			jlbec@...lplan.org
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