Messages in this thread | | | Date | Fri, 19 Mar 2004 20:58:46 +1100 | From | Nick Piggin <> | Subject | Re: [BENCHMARKS] 2.6.4 vs 2.6.4-mm1 |
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Ingo Molnar wrote:
>* Nick Piggin <piggin@cyberone.com.au> wrote: > > >>volanomark (MPS): >>This one starts getting huge mmap_sem contention at 150+ coming >>from futexes. Don't know what is taking the mmap_sem for writing. >>Maybe just brk or mmap. >> > >are you sure it's down_write() contention? down_read() can create >contention just as much, simply due to the fact that hundreds of threads >and a dozen CPUs are pounding in on the same poor lock. > >
No I'm not sure actually, it could be just read lock contention. IIRC it was all coming from the semaphore's spinlock, in up_read...
>i do think there should be a rw-semaphore variant that is per-cpu for >the read path. (This would also fix the 4:4 threading overhead.) > >
That would be interesting, yes. I have (somewhere) a patch that wakes up the semaphore's waiters outside its spinlock. I think that only gave about 5% or so improvement though.
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