Re: [PATCH 1/2] ipc semaphores: reduce ipc_lock contention in semtimedop

Nick Piggin
2010-04-13T20:05:32Z

On Tue, Apr 13, 2010 at 03:38:01PM -0400, Chris Mason wrote:
> On Wed, Apr 14, 2010 at 05:25:51AM +1000, Nick Piggin wrote:
> > I didn't notice anything that should make that go faster?
>
> Since I'm avoiding the ipc lock while operating on the array, it'll help
> any workload that hits on two or more semaphores in the array at
> once.

Yeah, I don't think SAP did that, significantly to matter. Possibly
some (aside from Oracle of course), do though.

> > Yes, with such a workload, using semops is basically legacy and simple
> > mutexes should work better. So I'm not outright against improving sysv
> > sem performance for more complex cases where nothing else we have works
> > as well.
> >
>
> I'm not in a hurry to overhaul a part of the kernel that has been stable
> for a long time. But it really needs some love I think. I'll have more
> numbers from a tpc run later this week.

Yep, I'm not against it. "industry standard benchmark" numbers would
be great.

I do think we need to be really careful with semantics though. The
API's been around for long enough that it is going to have been
(ab)used in every way possible :)