From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f172.google.com (mail-pd0-f172.google.com [209.85.192.172]) by kanga.kvack.org (Postfix) with ESMTP id 8DAD66B0031 for ; Wed, 9 Oct 2013 02:15:58 -0400 (EDT) Received: by mail-pd0-f172.google.com with SMTP id z10so432399pdj.3 for ; Tue, 08 Oct 2013 23:15:58 -0700 (PDT) Received: by mail-ee0-f54.google.com with SMTP id e53so139739eek.27 for ; Tue, 08 Oct 2013 23:15:54 -0700 (PDT) Date: Wed, 9 Oct 2013 08:15:51 +0200 From: Ingo Molnar Subject: Re: [PATCH v8 0/9] rwsem performance optimizations Message-ID: <20131009061551.GD7664@gmail.com> References: <1380753493.11046.82.camel@schen9-DESK> <20131003073212.GC5775@gmail.com> <1381186674.11046.105.camel@schen9-DESK> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1381186674.11046.105.camel@schen9-DESK> Sender: owner-linux-mm@kvack.org List-ID: To: Tim Chen Cc: Ingo Molnar , Andrew Morton , Linus Torvalds , Andrea Arcangeli , Alex Shi , Andi Kleen , Michel Lespinasse , Davidlohr Bueso , Matthew R Wilcox , Dave Hansen , Peter Zijlstra , Rik van Riel , Peter Hurley , "Paul E.McKenney" , Jason Low , Waiman Long , linux-kernel@vger.kernel.org, linux-mm * Tim Chen wrote: > Ingo, > > I ran the vanilla kernel, the kernel with all rwsem patches and the > kernel with all patches except the optimistic spin one. I am listing > two presentations of the data. Please note that there is about 5% > run-run variation. > > % change in performance vs vanilla kernel > #threads all without optspin > mmap only > 1 1.9% 1.6% > 5 43.8% 2.6% > 10 22.7% -3.0% > 20 -12.0% -4.5% > 40 -26.9% -2.0% > mmap with mutex acquisition > 1 -2.1% -3.0% > 5 -1.9% 1.0% > 10 4.2% 12.5% > 20 -4.1% 0.6% > 40 -2.8% -1.9% Silly question: how do the two methods of starting N threads compare to each other? Do they have identical runtimes? I think PeterZ's point was that the pthread_mutex case, despite adding extra serialization, actually runs faster in some circumstances. Also, mind posting the testcase? What 'work' do the threads do - clear some memory area? How big is the memory area? I'd expect this to be about large enough mmap()s showing page fault processing to be mmap_sem bound and the serialization via pthread_mutex() sets up a 'train' of threads in one case, while the parallel startup would run into the mmap_sem in the regular case. So I'd expect this to be a rather sensitive workload and you'd have to actively engineer it to hit the effect PeterZ mentioned. I could imagine MPI workloads to run into such patterns - but not deterministically. Only once you've convinced yourself that you are hitting that kind of effect reliably on the vanilla kernel, could/should the effects of an improved rwsem implementation be measured. Thanks, 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