Re: [PATCH 0/11] Per-bdi writeback flusher threads v9

Chris Mason
2009-06-06T00:19:29Z

On Fri, Jun 05, 2009 at 11:14:38PM +0200, Jan Kara wrote:
> On Fri 05-06-09 21:15:28, Jens Axboe wrote:
> > On Fri, Jun 05 2009, Frederic Weisbecker wrote:
> > > The result with noop is even more impressive.
> > >
> > > See: http://kernel.org/pub/linux/kernel/people/frederic/dbench-noop.pdf
> > >
> > > Also a comparison, noop with pdflush against noop with bdi writeback:
> > >
> > > http://kernel.org/pub/linux/kernel/people/frederic/dbench-noop-cmp.pdf
> >
> > OK, so things aren't exactly peachy here to begin with. It may not
> > actually BE an issue, or at least now a new one, but that doesn't mean
> > that we should not attempt to quantify the impact.
> What looks interesting is also the overall throughput. With pdflush we
> get to 2.5 MB/s + 26 MB/s while with per-bdi we get to 2.7 MB/s + 13 MB/s.
> So per-bdi seems to be *more* fair but throughput suffers a lot (which
> might be inevitable due to incurred seeks).
> Frederic, how much does dbench achieve for you just on one partition
> (test both consecutively if possible) with as many threads as have those
> two dbench instances together? Thanks.

Is the graph showing us dbench tput or disk tput? I'm assuming it is
disk tput, so bdi may just be writing less?

-chris