From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Fri, 11 May 2007 17:56:21 +0200 From: Ingo Molnar Subject: Re: [PATCH 0/2] convert mmap_sem to a scalable rw_mutex Message-ID: <20070511155621.GA13150@elte.hu> References: <20070511131541.992688403@chello.nl> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070511131541.992688403@chello.nl> Sender: owner-linux-mm@kvack.org Return-Path: To: Peter Zijlstra Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Oleg Nesterov , Andrew Morton , Thomas Gleixner , Nick Piggin List-ID: * Peter Zijlstra wrote: > I was toying with a scalable rw_mutex and found that it gives ~10% > reduction in system time on ebizzy runs (without the MADV_FREE patch). > > 2-way x86_64 pentium D box: > > 2.6.21 > > /usr/bin/time ./ebizzy -m -P > 59.49user 137.74system 1:49.22elapsed 180%CPU (0avgtext+0avgdata 0maxresident)k > 0inputs+0outputs (0major+33555877minor)pagefaults 0swaps > > 2.6.21-rw_mutex > > /usr/bin/time ./ebizzy -m -P > 57.85user 124.30system 1:42.99elapsed 176%CPU (0avgtext+0avgdata 0maxresident)k > 0inputs+0outputs (0major+33555877minor)pagefaults 0swaps nice! This 6% runtime reduction on a 2-way box will i suspect get exponentially better on systems with more CPUs/cores. i also like the design, alot: instead of doing a full new lock type (with per-arch changes, extra lockdep support, etc. etc) you layered the new abstraction ontop of mutexes. This makes this hard locking abstraction look really, really simple, while the percpu_counter trick makes it scale _perfectly_ for the reader case. Congratulations! given how nice this looks already, have you considered completely replacing rwsems with this? I suspect you could test the correctness of that without doing a mass API changeover, by embedding struct rw_mutex in struct rwsem and implementing kernel/rwsem.c's API that way. (the real patch would just flip it all over to rw-mutexes) Ingo -- 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