[Btrfs-devel] I/O idleness during postmark

[Chris Mason]

On Saturday 16 February 2008, Dongjun Shin wrote:
> 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.

Great to hear, thanks.

-chris