linux-ext4 - Re: [PATCH 1/2] ext2: speed up file creates by optimizing rec

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Message-Id: <20101207130708.71c894e9.akpm@linux-foundation.org>
Date:	Tue, 7 Dec 2010 13:07:08 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Eric Sandeen <sandeen@...hat.com>
Cc:	ext4 development <linux-ext4@...r.kernel.org>,
	Jan Kara <jack@...e.cz>
Subject: Re: [PATCH 1/2] ext2: speed up file creates by optimizing rec_len
 functions

On Tue, 07 Dec 2010 11:51:05 -0600
Eric Sandeen <sandeen@...hat.com> wrote:

> The addition of 64k block capability in the rec_len_from_disk
> and rec_len_to_disk functions added a bit of math overhead which
> slows down file create workloads needlessly when the architecture
> cannot even support 64k blocks, thanks to page size limits.
> 
> The directory entry checking can also be optimized a bit
> by sprinkling in some unlikely() conditions to move the
> error handling out of line.
> 
> bonnie++ sequential file creates on a 512MB ramdisk speeds up
> from about 2200/s to about 2500/s, about a 14% improvement.
> 

hrm, that's an improbably-large sounding improvement from eliminating
just a few test-n-branches from a pretty heavyweight operation.

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