From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753052Ab1GVBik (ORCPT ); Thu, 21 Jul 2011 21:38:40 -0400 Received: from smtp-out.google.com ([74.125.121.67]:46327 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751599Ab1GVBig convert rfc822-to-8bit (ORCPT ); Thu, 21 Jul 2011 21:38:36 -0400 DomainKey-Signature: a=rsa-sha1; s=beta; d=google.com; c=nofws; q=dns; h=dkim-signature:mime-version:in-reply-to:references:from:date: message-id:subject:to:cc:content-type: content-transfer-encoding:x-system-of-record; b=gWo76SntyEe7u/ZL8+vPSWBeKKuqW77A1tn5qA5WVBE9+oGmKqLm0RZRaYaBr9+z4 9K1pJ3XpQTEWY9hbfVbzA== MIME-Version: 1.0 In-Reply-To: <20110722011747.GB2807@redhat.com> References: <20110722003211.GA2807@redhat.com> <20110722011747.GB2807@redhat.com> From: Paul Turner Date: Thu, 21 Jul 2011 18:38:01 -0700 Message-ID: Subject: Re: [RFT][patch 17/18] sched: use jump labels to reduce overhead when bandwidth control is inactive To: Jason Baron Cc: linux-kernel@vger.kernel.org, Peter Zijlstra , Bharata B Rao , Dhaval Giani , Balbir Singh , Vaidyanathan Srinivasan , Srivatsa Vaddagiri , Kamalesh Babulal , Hidetoshi Seto , Ingo Molnar , Pavel Emelyanov , rth@redhat.com Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT X-System-Of-Record: true Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 21, 2011 at 6:17 PM, Jason Baron wrote: > On Thu, Jul 21, 2011 at 05:57:31PM -0700, Paul Turner wrote: >> On Thu, Jul 21, 2011 at 5:32 PM, Jason Baron wrote: >> > rth@redhat.com >> > Bcc: >> > Subject: Re: [RFT][patch 17/18] sched: use jump labels to reduce overhead >> >  when bandwidth control is inactive >> > Reply-To: >> > In-Reply-To: <20110721184758.403388616@google.com> >> > >> > On Thu, Jul 21, 2011 at 09:43:42AM -0700, Paul Turner wrote: >> >> So I'm seeing some strange costs associated with jump_labels; while on paper >> >> the branches and instructions retired improves (as expected) we're taking an >> >> unexpected hit in IPC. >> >> >> >> [From the initial mail we have workloads: >> >>   mkdir -p /cgroup/cpu/test >> >>   echo $$ > /dev/cgroup/cpu/test (only cpu,cpuacct mounted) >> >>   (W1) taskset -c 0 perf stat --repeat 50 -e instructions,cycles,branches bash -c "for ((i=0;i<5;i++)); do $(dirname $0)/pipe-test 20000; done" >> >>   (W2)taskset -c 0 perf stat --repeat 50 -e instructions,cycles,branches bash -c "$(dirname $0)/pipe-test 100000;true" >> >>   (W3)taskset -c 0 perf stat --repeat 50 -e instructions,cycles,branches bash -c "$(dirname $0)/pipe-test 100000;" >> >> ] >> >> >> >> To make some of the figures more clear: >> >> >> >> Legend: >> >> !BWC = tip + bwc, BWC compiled out >> >> BWC = tip + bwc >> >> BWC_JL = tip + bwc + jump label (this patch) >> >> >> >> >> >> Now, comparing under W1 we see: >> >> W1: BWC vs BWC_JL >> >>                             instructions            cycles                  branches              elapsed >> >> --------------------------------------------------------------------------------------------------------------------- >> >> clovertown [BWC]            845934117               974222228               152715407             0.419014188 [baseline] >> >> +unconstrained              857963815 (+1.42)      1007152750 (+3.38)       153140328 (+0.28)     0.433186926 (+3.38)  [rel] >> >> +10000000000/1000:          876937753 (+2.55)      1033978705 (+5.65)       160038434 (+3.59)     0.443638365 (+5.66)  [rel] >> >> +10000000000/1000000:       880276838 (+3.08)      1036176245 (+6.13)       160683878 (+4.15)     0.444577244 (+6.14)  [rel] >> >> >> >> barcelona [BWC]             820573353               748178486               148161233             0.342122850 [baseline] >> >> +unconstrained              817011602 (-0.43)       759838181 (+1.56)       145951513 (-1.49)     0.347462571 (+1.56)  [rel] >> >> +10000000000/1000:          830109086 (+0.26)       770451537 (+1.67)       151228902 (+1.08)     0.350824677 (+1.65)  [rel] >> >> +10000000000/1000000:       830196206 (+0.30)       770704213 (+2.27)       151250413 (+1.12)     0.350962182 (+2.28)  [rel] >> >> >> >> westmere [BWC]              802533191               694415157               146071233             0.194428018 [baseline] >> >> +unconstrained              799057936 (-0.43)       751384496 (+8.20)       143875513 (-1.50)     0.211182620 (+8.62)  [rel] >> >> +10000000000/1000:          812033785 (+0.27)       761469084 (+8.51)       149134146 (+1.09)     0.212149229 (+8.28)  [rel] >> >> +10000000000/1000000:       811912834 (+0.27)       757842988 (+7.45)       149113291 (+1.09)     0.211364804 (+7.30)  [rel] >> >> e.g. Barcelona issues ~0.43% less instructions, for a total of 817011602, in >> >> the unconstrained case with BWC. >> >> >> >> >> >> Where "unconstrained, 10000000000/1000, 10000000000/10000" are the on >> >> measurements for BWC_JL, with (%d) being the relative difference to their >> >> BWC counterparts. >> >> >> >> W1: BWC vs BWC_JL is very similar. >> >>       BWC vs BWC_JL >> >> clovertown [BWC]            985732031              1283113452               175621212             1.375905653 >> >> +unconstrained              979242938 (-0.66)      1288971141 (+0.46)       172122546 (-1.99)     1.389795165 (+1.01)  [rel] >> >> +10000000000/1000:          999886468 (+0.33)      1296597143 (+1.13)       180554004 (+1.62)     1.392576770 (+1.18)  [rel] >> >> +10000000000/1000000:       999034223 (+0.11)      1293925500 (+0.57)       180413829 (+1.39)     1.391041338 (+0.94)  [rel] >> >> >> >> barcelona [BWC]             982139920              1078757792               175417574             1.069537049 >> >> +unconstrained              965443672 (-1.70)      1075377223 (-0.31)       170215844 (-2.97)     1.045595065 (-2.24)  [rel] >> >> +10000000000/1000:          989104943 (+0.05)      1100836668 (+0.52)       178837754 (+1.22)     1.058730316 (-1.77)  [rel] >> >> +10000000000/1000000:       987627489 (-0.32)      1095843758 (-0.17)       178567411 (+0.84)     1.056100899 (-2.28)  [rel] >> >> >> >> westmere [BWC]              918633403               896047900               166496917             0.754629182 >> >> +unconstrained              914740541 (-0.42)       903906801 (+0.88)       163652848 (-1.71)     0.758050332 (+0.45)  [rel] >> >> +10000000000/1000:          927517377 (-0.41)       952579771 (+5.67)       170173060 (+0.75)     0.771193786 (+2.43)  [rel] >> >> +10000000000/1000000:       914676985 (-0.89)       936106277 (+3.81)       167683288 (+0.22)     0.764973632 (+1.38)  [rel] >> >> >> >> Now this is rather odd, almost across the board we're seeing the expected >> >> drops in instructions and branches, yet we appear to be paying a heavy IPC >> >> price.  The fact that wall-time has scaled equivalently with cycles roughly >> >> rules out the cycles counter being off. >> >> > > if i understand your results, for barcelona you did see an improvement > in cycles and eslapsed time with jump labels for unconstrained? > Under W2, yes. >> >> We are seeing the expected behavior in the bandwidth enabled case; >> >> specifically the blocks are taking an extra branch >> >> and instruction which shows up on all the numbers above. >> >> >> >> With respect to compiler mangling the text is essentially unchanged in size. >> >> One lurking suspicion is whether the inserted nops have perturbed some of the >> >> jmp/branch alignments? > > hmmmm....not sure, I'm adding Richard Henderson, to the 'cc list, who > worked on the 'asm goto' in gcc. > >> >> >> >>     text    data     bss     dec     hex filename >> >>  7277206 2827256 2125824 12230286         ba9e8e vmlinux.jump_label >> >>  7276886 2826744 2125824 12229454         ba9b4e vmlinux.no_jump_label >> >> > > the other thing here is that vmlinux.jump_label includes the extra > kernel/jump_label.o file, so you can sort of subtract the text size of > that file to do a fair comparison. Even without doing that it's only a 1.00004% change in text size. I was just making the inference that if it's gcc mangling it's likely in the layout/alignment. > > Also, I would have expected the data section to have increased more with > jump labels enabled. Are tracepoints disabled (a current user of jump > labels). Yeah -- Tracing is enabled so the BWC build should have labels already; this likely accounts for the small increase noted above. > >> >>  I have checked to make sure that the right instructions are being patched in >> >>  at run-time.  I've also pulled a fully patched jump_label out of the kernel >> >>  into a userspace test (and benchmarked it directly under perf).  The results >> >>  here are also exactly as expected. >> >> >> >> e.g. >> >>  Performance counter stats for './jump_test': >> >>      1,500,839,002 instructions, 300,147,081 branches 702,468,404 cycles >> >> Performance counter stats for './jump_test 1': >> >>      2,001,014,609 instructions, 400,177,192 branches 901,758,219 cycles >> >> > > what no-op did you use in userspace? I wouldn't think the no-op choice > would make any difference though...At compile time we use a 'jmp 0', and > then at boot we dynamically patch the 'jmp 0' with the no-op we think works > best... > Sorry -- what I meant here is I pulled the run-time chosen "best" nop out of /proc/kcore and tested a tight loop about a sequence (e.g. cfs_rq_throttled()) with JL being the nop and jmp respectively. Specifically for Westmere this ends up being K8_NOP5 -- 0x666666D0 > thanks, > > -Jason > >> >> Overall if we can fix the IPC the benefit in the globally unconstrained case >> >> looks really good. >> >> >> >> Any thoughts Jason? >> >> >> > >> > Do you have CONFIG_CC_OPTIMIZE_FOR_SIZE set? I know that when >> > CONFIG_CC_OPTIMIZE_FOR_SIZE is not set, the compiler can make the code >> > more optimal. >> > >> >> Ah I should have mentioned that was one of the holes I stared down: >> >> Builds were -O2 (gcc-4.6.1) and >> $  zcat /proc/config.gz | grep CONFIG_CC_OPTIMIZE_FOR_SIZE >> # CONFIG_CC_OPTIMIZE_FOR_SIZE is not set >> >> Same kernel image across all platforms. >> >> >> >> >> >> >> > thanks, >> > >> > -Jason >> > >> -- >> 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/ >