Messages in this thread |  | | | Date | Sun, 18 Dec 2005 23:28:43 -0500 (EST) | | From | Steven Rostedt <> | | Subject | Re: [patch 00/15] Generic Mutex Subsystem |
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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
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