Re: [BENCHMARKS] 2.6.4 vs 2.6.4-mm1

Ingo Molnar
2004-03-19T09:49:56Z

* 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.

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.)

Ingo