Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761534Ab3JPS2u (ORCPT ); Wed, 16 Oct 2013 14:28:50 -0400 Received: from mga09.intel.com ([134.134.136.24]:20996 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759264Ab3JPS2s (ORCPT ); Wed, 16 Oct 2013 14:28:48 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.93,508,1378882800"; d="scan'208";a="420164582" Subject: Re: [PATCH v8 0/9] rwsem performance optimizations From: Tim Chen To: Ingo Molnar 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 In-Reply-To: <20131016065526.GB22509@gmail.com> References: <1380753493.11046.82.camel@schen9-DESK> <20131003073212.GC5775@gmail.com> <1381186674.11046.105.camel@schen9-DESK> <20131009061551.GD7664@gmail.com> <1381336441.11046.128.camel@schen9-DESK> <20131010075444.GD17990@gmail.com> <1381882156.11046.178.camel@schen9-DESK> <20131016065526.GB22509@gmail.com> Content-Type: text/plain; charset="UTF-8" Date: Wed, 16 Oct 2013 11:28:34 -0700 Message-ID: <1381948114.11046.194.camel@schen9-DESK> Mime-Version: 1.0 X-Mailer: Evolution 2.32.3 (2.32.3-1.fc14) Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 7795 Lines: 220 On Wed, 2013-10-16 at 08:55 +0200, Ingo Molnar wrote: > * Tim Chen wrote: > > > On Thu, 2013-10-10 at 09:54 +0200, Ingo Molnar wrote: > > > * Tim Chen wrote: > > > > > > > The throughput of pure mmap with mutex is below vs pure mmap is below: > > > > > > > > % change in performance of the mmap with pthread-mutex vs pure mmap > > > > #threads vanilla all rwsem without optspin > > > > patches > > > > 1 3.0% -1.0% -1.7% > > > > 5 7.2% -26.8% 5.5% > > > > 10 5.2% -10.6% 22.1% > > > > 20 6.8% 16.4% 12.5% > > > > 40 -0.2% 32.7% 0.0% > > > > > > > > So with mutex, the vanilla kernel and the one without optspin both run > > > > faster. This is consistent with what Peter reported. With optspin, the > > > > picture is more mixed, with lower throughput at low to moderate number > > > > of threads and higher throughput with high number of threads. > > > > > > So, going back to your orignal table: > > > > > > > % change in performance of the mmap with pthread-mutex vs pure mmap > > > > #threads vanilla all without optspin > > > > 1 3.0% -1.0% -1.7% > > > > 5 7.2% -26.8% 5.5% > > > > 10 5.2% -10.6% 22.1% > > > > 20 6.8% 16.4% 12.5% > > > > 40 -0.2% 32.7% 0.0% > > > > > > > > In general, vanilla and no-optspin case perform better with > > > > pthread-mutex. For the case with optspin, mmap with pthread-mutex is > > > > worse at low to moderate contention and better at high contention. > > > > > > it appears that 'without optspin' appears to be a pretty good choice - if > > > it wasn't for that '1 thread' number, which, if I correctly assume is the > > > uncontended case, is one of the most common usecases ... > > > > > > How can the single-threaded case get slower? None of the patches should > > > really cause noticeable overhead in the non-contended case. That looks > > > weird. > > > > > > It would also be nice to see the 2, 3, 4 thread numbers - those are the > > > most common contention scenarios in practice - where do we see the first > > > improvement in performance? > > > > > > Also, it would be nice to include a noise/sttdev figure, it's really hard > > > to tell whether -1.7% is statistically significant. > > > > Ingo, > > > > I think that the optimistic spin changes to rwsem should enhance > > performance to real workloads after all. > > > > In my previous tests, I was doing mmap followed immediately by > > munmap without doing anything to the memory. No real workload > > will behave that way and it is not the scenario that we > > should optimize for. A much better approximation of > > real usages will be doing mmap, then touching > > the memories being mmaped, followed by munmap. > > That's why I asked for a working testcase to be posted ;-) Not just > pseudocode - send the real .c thing please. I was using a modified version of Anton's will-it-scale test. I'll try to port the tests to perf bench to make it easier for other people to run the tests. > > > This changes the dynamics of the rwsem as we are now dominated by read > > acquisitions of mmap sem due to the page faults, instead of having only > > write acquisitions from mmap. [...] > > Absolutely, the page fault read case is the #1 optimization target of > rwsems. > > > [...] In this case, any delay in write acquisitions will be costly as we > > will be blocking a lot of readers. This is where optimistic spinning on > > write acquisitions of mmap sem can provide a very significant boost to > > the throughput. > > > > I change the test case to the following with writes to > > the mmaped memory: > > > > #define MEMSIZE (1 * 1024 * 1024) > > > > char *testcase_description = "Anonymous memory mmap/munmap of 1MB"; > > > > void testcase(unsigned long long *iterations) > > { > > int i; > > > > while (1) { > > char *c = mmap(NULL, MEMSIZE, PROT_READ|PROT_WRITE, > > MAP_PRIVATE|MAP_ANONYMOUS, -1, 0); > > assert(c != MAP_FAILED); > > for (i=0; i > c[i] = 0xa; > > } > > munmap(c, MEMSIZE); > > > > (*iterations)++; > > } > > } > > It would be _really_ nice to stick this into tools/perf/bench/ as: > > perf bench mem pagefaults > > or so, with a number of parallelism and workload patterns. See > tools/perf/bench/numa.c for a couple of workload generators - although > those are not page fault intense. > > So that future generations can run all these tests too and such. Okay, will do. > > > I compare the throughput where I have the complete rwsem patchset > > against vanilla and the case where I take out the optimistic spin patch. > > I have increased the run time by 10x from my pervious experiments and do > > 10 runs for each case. The standard deviation is ~1.5% so any changes > > under 1.5% is statistically significant. > > > > % change in throughput vs the vanilla kernel. > > Threads all No-optspin > > 1 +0.4% -0.1% > > 2 +2.0% +0.2% > > 3 +1.1% +1.5% > > 4 -0.5% -1.4% > > 5 -0.1% -0.1% > > 10 +2.2% -1.2% > > 20 +237.3% -2.3% > > 40 +548.1% +0.3% > > The tail is impressive. The early parts are important as well, but it's > really hard to tell the significance of the early portion without having > an sttdev column. Here's the data with sdv column: n all sdv No-optspin sdv 1 +0.4% 0.9% -0.1% 0.8% 2 +2.0% 0.8% +0.2% 1.2% 3 +1.1% 0.8% +1.5% 0.6% 4 -0.5% 0.9% -1.4% 1.1% 5 -0.1% 1.1% -0.1% 1.1% 10 +2.2% 0.8% -1.2% 1.0% 20 +237.3% 0.7% -2.3% 1.3% 40 +548.1% 0.8% +0.3% 1.2% > ( "perf stat --repeat N" will give you sttdev output, in handy percentage > form. ) > > > Now when I test the case where we acquire mutex in the > > user space before mmap, I got the following data versus > > vanilla kernel. There's little contention on mmap sem > > acquisition in this case. > > > > n all No-optspin > > 1 +0.8% -1.2% > > 2 +1.0% -0.5% > > 3 +1.8% +0.2% > > 4 +1.5% -0.4% > > 5 +1.1% +0.4% > > 10 +1.5% -0.3% > > 20 +1.4% -0.2% > > 40 +1.3% +0.4% Adding std-dev to above data: n all sdv No-optspin sdv 1 +0.8% 1.0% -1.2% 1.2% 2 +1.0% 1.0% -0.5% 1.0% 3 +1.8% 0.7% +0.2% 0.8% 4 +1.5% 0.8% -0.4% 0.7% 5 +1.1% 1.1% +0.4% 0.3% 10 +1.5% 0.7% -0.3% 0.7% 20 +1.4% 0.8% -0.2% 1.0% 40 +1.3% 0.7% +0.4% 0.5% > > > > Thanks. > > A bit hard to see as there's no comparison _between_ the pthread_mutex and > plain-parallel versions. No contention isn't a great result if performance > suffers because it's all serialized. Now the data for pthread-mutex vs plain-parallel vanilla testcase with std-dev n vanilla sdv Rwsem-all sdv No-optspin sdv 1 +0.5% 0.9% +1.4% 0.9% -0.7% 1.0% 2 -39.3% 1.0% -38.7% 1.1% -39.6% 1.1% 3 -52.6% 1.2% -51.8% 0.7% -52.5% 0.7% 4 -59.8% 0.8% -59.2% 1.0% -59.9% 0.9% 5 -63.5% 1.4% -63.1% 1.4% -63.4% 1.0% 10 -66.1% 1.3% -65.6% 1.3% -66.2% 1.3% 20 +178.3% 0.9% +182.3% 1.0% +177.7% 1.1% 40 +604.8% 1.1% +614.0% 1.0% +607.9% 0.9% The version with full rwsem patchset perform best across the threads. Serialization actually hurts for smaller number of threads even for current vanilla kernel. I'll rerun the tests once I ported them to the perf bench. It may take me a couple of days. Thanks. Tim -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/