Re: [RFC PATCH 0/5] futex: introduce an optimistic spinning futex

From: Davidlohr Bueso
Date: Mon Jul 21 2014 - 20:33:17 EST


On Mon, 2014-07-21 at 14:31 -0700, Andy Lutomirski wrote:
> On Mon, Jul 21, 2014 at 2:27 PM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> > All this is predicated on the fact that syscalls are 'expensive'.
> > Weren't syscalls only 100s of cycles? All this bitmap mucking is far
> > more expensive due to cacheline misses, which due to the size of the
> > things is almost guaranteed.
>
> 120 - 300 cycles for me, unless tracing happens, and I'm working on
> reducing the incidence of tracing.

fwiw here's what lmbench's lat_ctx says on my system . For 'accuracy', I
kept the runs short.

http://www.stgolabs.net/lat_ctx.png

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/