Re: [PATCH] qla2xxx: Resolved a performance issue in interrupt

Matthew Wilcox
2009-06-10T19:48:10Z

On Wed, Jun 10, 2009 at 07:10:18PM +0000, James Bottomley wrote:
> > That's a curious observation... I'm just trying to understand the
> > numbers here, but, are we sure that this spin_lock() ->
> > spin_lock_irqsave() conversion is in fact the mitigating factor.
>
> I think so ... the performance of both fixes is actually nearly
> identical showing that the base reason (interrupt while holding hardware
> spinlock adding to latency) is the correct one.
>
> The curiosity I had is whether we can do even better by disabling
> interrupts for the whole of the ISR rather than only over the sections
> where we take the hw lock, and I don't think we have conclusive evidence
> either way on that.

It probably doesn't matter much either way. At some point, I think
Peter will be successful in forcing IRQF_DISABLED for all interrupts,
and this decision will go away.

--
Matthew Wilcox Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours. We can't possibly take such
a retrograde step."