On Wed, 2011-11-09 at 03:31 -0500, Christoph Hellwig wrote:
> On Tue, Nov 08, 2011 at 10:28:07PM -0800, Nicholas A. Bellinger wrote:
> > Hi Christoph,
> >
> > What extra parameters do you recommend using for the alloc_workqueue()
> > setup here..?
> >
> > While doing some initial fio large block performance tests with a 2x
> > port 8 Gb/sec 25xx parts with this evening, I noticed the per HW port
> > qla_tgt->qla_tgt_wq workqueues using alloc_workqueue("qla_tgt_wq,
> > WQ_UNBOUND, 1); seem to have a slight performance edge over this patch
> > to start using a single global qla_tgt_wq setup in qla_target.c with
> > alloc_workqueue("qla_tgt_wq, 0, 0).
> >
> > It's on the order of a ~300 MB/sec difference between the two, with the
> > per qla_tgt->qla_tgt_wq running very near what the backend is capable of
> > at ~1500 MB/sec, and this patch to convert to a single qla_tgt_wq with
> > the same tests are ~1200 MB/sec.
> >
> > For the slower case with this patch, a single kworker thread is running
> > @ 100% CPU utilization with the wq defaults. Using per HW port context
> > qla_tgt->qla_tgt_wq with WQ_UNBOUND, 1, multiple kworkers are running at
> > ~40% utilization, and AFAICT seem to be doing a better job of
> > distributing load across multiple qla_hw_data ports.
> >
> > Any thoughts on what might be limiting the single global qla_tgt_wq in
> > this patch against per HW port qla_tgt_wq dispatch..?
>
> Read through Documentation/workqueue.txt. It sounds like this workqueue
> is CPU bound, although I wonder why. Can you look at perf top and see
> were we spend the time?
Yes, I've been reading through Documentation/workqueue.txt, and just
wanted so see what alloc_workqueue() parameters you thought this type of
setup should be using.
Anywyas, will have a look at this with perf later today using the same
alloc_workqueue() defaults..
--nab
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