lkml.org 
[lkml]   [2005]   [Dec]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [patch 00/15] Generic Mutex Subsystem

On Mon, 19 Dec 2005, Andi Kleen wrote:

> > $ ./test-mutex V 16 10 $ ./test-mutex V 16 10
> > 8 CPUs, running 16 tasks. 8 CPUs, running 16 tasks.
> > checking VFS performance. checking VFS performance.
> > avg loops/sec: 34713 avg loops/sec: 84153
> > CPU utilization: 63% CPU utilization: 22%
> >
> > i.e. in this workload, the mutex based kernel was 2.4 times faster
> > than the semaphore based kernel, _and_ it also had 2.8 times less CPU
> > utilization. (In terms of 'ops per CPU cycle', the semaphore kernel
> > performed 551 ops/sec per 1% of CPU time used, while the mutex kernel
> > performed 3825 ops/sec per 1% of CPU time used - it was 6.9 times
> > more efficient.)
>
> Do you have an idea where this big difference comes from? It doesn't look
> it's from the fast path which is essentially the same. Do the mutexes have
> that much better scheduling behaviour than semaphores? It is a bit hard to
> believe.
>
> I would perhaps understand your numbers if you used adaptive mutexes
> or similar that spin for a bit, but just for pure sleeping locks it seems
> weird. After all the scheduler should work in the same way for both.
>

Perhaps it's the smaller structures, as Ingo said, which would allow for
better cache handling.

-- Steve

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

\
 
 \ /
  Last update: 2005-12-19 05:31    [from the cache]
©2003-2014 Jasper Spaans. Advertise on this site