From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 5 Apr 2007 11:06:01 +0200 From: Eric Dumazet Subject: Re: missing madvise functionality Message-Id: <20070405110601.8ef4b601.dada1@cosmosbay.com> In-Reply-To: <4614B3FB.2090405@redhat.com> References: <46128051.9000609@redhat.com> <46128CC2.9090809@redhat.com> <20070403172841.GB23689@one.firstfloor.org> <20070403125903.3e8577f4.akpm@linux-foundation.org> <4612B645.7030902@redhat.com> <20070403202937.GE355@devserv.devel.redhat.com> <4614A5CC.5080508@redhat.com> <20070405100848.db97d835.dada1@cosmosbay.com> <4614B3FB.2090405@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Rik van Riel Cc: Jakub Jelinek , Ulrich Drepper , Andrew Morton , Andi Kleen , Linux Kernel , linux-mm@kvack.org, Hugh Dickins List-ID: On Thu, 05 Apr 2007 04:31:55 -0400 Rik van Riel 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, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org