From mboxrd@z Thu Jan 1 00:00:00 1970 From: Neil Horman Subject: Re: [PATCH] x86: Run checksumming in parallel accross multiple alu's Date: Fri, 1 Nov 2013 10:06:55 -0400 Message-ID: <20131101140655.GA8467@hmsreliant.think-freely.org> References: <20131029114907.GE24477@neilslaptop.think-freely.org> <20131029125233.GA17449@gmail.com> <20131029130712.GA25078@neilslaptop.think-freely.org> <20131029131149.GB20408@gmail.com> <20131029141706.GC25078@neilslaptop.think-freely.org> <20131029142716.GA28113@gmail.com> <20131029202644.GB32389@localhost.localdomain> <20131031102200.GA10098@gmail.com> <20131031143325.GB25894@hmsreliant.think-freely.org> <20131101091337.GA27063@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Eric Dumazet , linux-kernel@vger.kernel.org, sebastien.dugue@bull.net, Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , x86@kernel.org, netdev@vger.kernel.org To: Ingo Molnar Return-path: Content-Disposition: inline In-Reply-To: <20131101091337.GA27063@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Fri, Nov 01, 2013 at 10:13:37AM +0100, Ingo Molnar wrote: > > * Neil Horman wrote: > > > On Thu, Oct 31, 2013 at 11:22:00AM +0100, Ingo Molnar wrote: > > > > > > * Neil Horman wrote: > > > > > > > > etc. For such short runtimes make sure the last column displays > > > > > close to 100%, so that the PMU results become trustable. > > > > > > > > > > A nehalem+ PMU will allow 2-4 events to be measured in parallel, > > > > > plus generics like 'cycles', 'instructions' can be added 'for free' > > > > > because they get counted in a separate (fixed purpose) PMU register. > > > > > > > > > > The last colum tells you what percentage of the runtime that > > > > > particular event was actually active. 100% (or empty last column) > > > > > means it was active all the time. > > > > > > > > > > Thanks, > > > > > > > > > > Ingo > > > > > > > > > > > > > Hmm, > > > > > > > > I ran this test: > > > > > > > > for i in `seq 0 1 3` > > > > do > > > > echo $i > /sys/module/csum_test/parameters/module_test_mode > > > > taskset -c 0 perf stat --repeat 20 -C 0 -e L1-dcache-load-misses -e L1-dcache-prefetches -e cycles -e instructions -ddd ./test.sh > > > > done > > > > > > You need to remove '-ddd' which is a shortcut for a ton of useful > > > events, but here you want to use fewer events, to increase the > > > precision of the measurement. > > > > > > Thanks, > > > > > > Ingo > > > > > > > Thank you ingo, that fixed it. I'm trying some other variants of > > the csum algorithm that Doug and I discussed last night, but FWIW, > > the relative performance of the 4 test cases > > (base/prefetch/parallel/both) remains unchanged. I'm starting to > > feel like at this point, theres very little point in doing > > parallel alu operations (unless we can find a way to break the > > dependency on the carry flag, which is what I'm tinkering with > > now). > > I would still like to encourage you to pick up the improvements that > Doug measured (mostly via prefetch tweaking?) - that looked like > some significant speedups that we don't want to lose! > Well, yes, I made a line item of that in my subsequent note below. I'm going to repost that shortly, and I suggested that we revisit this when the AVX instruction extensions are available. > Also, trying to stick the in-kernel implementation into 'perf bench' > would be a useful first step as well, for this and future efforts. > > See what we do in tools/perf/bench/mem-memcpy-x86-64-asm.S to pick > up the in-kernel assembly memcpy implementations: > Yes, I'll look into adding this as well Regards Neil