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Re: [Qemu-devel] [PATCH 1/4] block: add enable_write_cache flag
From: |
Christoph Hellwig |
Subject: |
Re: [Qemu-devel] [PATCH 1/4] block: add enable_write_cache flag |
Date: |
Wed, 2 Sep 2009 16:14:44 +0200 |
User-agent: |
Mutt/1.3.28i |
On Wed, Sep 02, 2009 at 08:13:52AM -0500, Anthony Liguori wrote:
> Does barrier=0 make a performance difference? IOW, would the typical
> default ext3 deployment show worse behavior?
I'll give it a spin.
> >A kernel defconfig compile takes between 9m40s and 9m42s with
> >data=writeback and barrieres disabled, and with fdatasync barriers
> >enabled it actually is minimally faster,
>
> If fdatasync different than fsync on ext3? Does it result in a full
> metadata commit?
ext3 honors the fdatasync flag and only does it's horrible job if the
metadata we care about is dirty, that is only if some non-timestamp
data is dirty. Which means for a non-sparse image file it does
well, while for a sparse image file needing allocations it will
cause trouble. And now that you mention it I've only tested the
non-sparse case which now is default for the management tools at
least on Fedora.