[Btrfs-devel] I/O idleness during postmark

[Chris Mason]

On Friday 15 February 2008, Dongjun Shin wrote:
> Hello,
>
> When I'm running postmark on btrfs v0.12, although the system
> must be busy doing the I/O, there are some cases where the I/O is idle
> while btrfs workqueue eats up most of the CPU time.
>

I wasn't able to reproduce this on my small ssd, but I could trigger it on my 
larger sata drive.  Most of the time we seem to be stuck in 
btrfs_realloc_node, which is part of the defrag.

The attached patch disables defrag in ssd mode, or you can grab the latest 
from btrfs-unstable:

http://oss.oracle.com/mercurial/mason/btrfs-unstable/archive/1cc5025e42bb.tar.gz

I had left defrag on in ssd mode because earlier tests showed it still helped 
in some read workloads.  This doesn't seem to be the case anymore, but if you 
see read regressions, please let me know.

(updated no-defrag patch below)

-chris
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