On Thu, 05 Apr 2007 04:31:55 -0400 Rik van Riel <[EMAIL PROTECTED]> wrote:
> Eric Dumazet wrote: > > > Could you please add this patch and see if it helps on your machine ? > > > > [PATCH] VM : mm_struct's mmap_cache should be close to mmap_sem > > > > Avoids cache line dirtying > > I could, but I already know it's not going to help much. > > How do I know this? I already have 66% idle time when running > with my patch (and without Nick Piggin's patch to take the > mmap_sem for reading only). Interestingly, despite the idle > time increasing from 10% to 66%, throughput triples... > > Saving some CPU time will probably only increase the idle time, > I see no reason your patch would reduce contention and increase > throughput. > > I'm not saying your patch doesn't make sense - it probably does. > I just suspect it would have zero impact on this particular > scenario, because of the already huge idle time. I know your cpus have idle time, that not the question. But *when* your cpus are not idle, they might be slowed down because of cache line transferts between them. This patch doesnt reduce contention, just latencies (and overall performance) I dont currently have SMP test machine, so I couldnt test it myself. On x86_64, I am pretty sure the patch would help, because offsetof(mmap_sem) = 0x60 On i386, offsetof(mmap_sem)=0x34, so this patch wont help. As you said, throughput can raise and idle time raise too. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
