[Btrfs-devel] I/O idleness during postmark

[Dongjun Shin]

On 2/16/08, Chris Mason <chris.mason at oracle.com> wrote:
> 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
>
>

There is no more I/O stall with the latest unstable version of btrfs.
Here's the postmark numbers for comparison (16k block size & ssd option).

- v0.12
file size 9-15kB, num files 10k, transaction 100k => 473 TPS
file size 9-15kB, num files 100k, transaction 100k => 84 TPS

- latest unstable
file size 9-15kB, num files 10k, transaction 100k => 483 TPS
file size 9-15kB, num files 100k, transaction 100k => 129 TPS

It seems that there is no read regression for postmark.

Thanks,

--
Dongjun