Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754334Ab2JPL1s (ORCPT ); Tue, 16 Oct 2012 07:27:48 -0400 Received: from shutemov.name ([176.9.204.213]:59951 "EHLO shutemov.name" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753527Ab2JPL1r (ORCPT ); Tue, 16 Oct 2012 07:27:47 -0400 Date: Tue, 16 Oct 2012 14:28:45 +0300 From: "Kirill A. Shutemov" To: Ni zhan Chen Cc: "Kirill A. Shutemov" , Andrew Morton , Andrea Arcangeli , linux-mm@kvack.org, Andi Kleen , "H. Peter Anvin" , linux-kernel@vger.kernel.org Subject: Re: [PATCH v4 00/10, REBASED] Introduce huge zero page Message-ID: <20121016112845.GA13540@shutemov.name> References: <1350280859-18801-1-git-send-email-kirill.shutemov@linux.intel.com> <507D2E83.4010702@gmail.com> <20121016105456.GA13265@shutemov.name> <507D4143.3020108@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <507D4143.3020108@gmail.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 9794 Lines: 172 On Tue, Oct 16, 2012 at 07:13:07PM +0800, Ni zhan Chen wrote: > On 10/16/2012 06:54 PM, Kirill A. Shutemov wrote: > >On Tue, Oct 16, 2012 at 05:53:07PM +0800, Ni zhan Chen wrote: > >>>By hpa request I've tried alternative approach for hzp implementation (see > >>>Virtual huge zero page patchset): pmd table with all entries set to zero > >>>page. This way should be more cache friendly, but it increases TLB > >>>pressure. > >>Thanks for your excellent works. But could you explain me why > >>current implementation not cache friendly and hpa's request cache > >>friendly? Thanks in advance. > >In workloads like microbenchmark1 you need N * size(zero page) cache > >space to get zero page fully cached, where N is cache associativity. > >If zero page is 2M, cache pressure is significant. > > > >On other hand with table of 4k zero pages (hpa's proposal) will increase > >pressure on TLB, since we have more pages for the same memory area. So we > >have to do more page translation in this case. > > > >On my test machine with simple memcmp() virtual huge zero page is faster. > >But it highly depends on TLB size, cache size, memory access and page > >translation costs. > > > >It looks like cache size in modern processors grows faster than TLB size. > > Oh, I see, thanks for your quick response. Another one question below， > > > > >>>The problem with virtual huge zero page: it requires per-arch enabling. > >>>We need a way to mark that pmd table has all ptes set to zero page. > >>> > >>>Some numbers to compare two implementations (on 4s Westmere-EX): > >>> > >>>Mirobenchmark1 > >>>============== > >>> > >>>test: > >>> posix_memalign((void **)&p, 2 * MB, 8 * GB); > >>> for (i = 0; i < 100; i++) { > >>> assert(memcmp(p, p + 4*GB, 4*GB) == 0); > >>> asm volatile ("": : :"memory"); > >>> } > >>> > >>>hzp: > >>> Performance counter stats for './test_memcmp' (5 runs): > >>> > >>> 32356.272845 task-clock # 0.998 CPUs utilized ( +- 0.13% ) > >>> 40 context-switches # 0.001 K/sec ( +- 0.94% ) > >>> 0 CPU-migrations # 0.000 K/sec > >>> 4,218 page-faults # 0.130 K/sec ( +- 0.00% ) > >>> 76,712,481,765 cycles # 2.371 GHz ( +- 0.13% ) [83.31%] > >>> 36,279,577,636 stalled-cycles-frontend # 47.29% frontend cycles idle ( +- 0.28% ) [83.35%] > >>> 1,684,049,110 stalled-cycles-backend # 2.20% backend cycles idle ( +- 2.96% ) [66.67%] > >>> 134,355,715,816 instructions # 1.75 insns per cycle > >>> # 0.27 stalled cycles per insn ( +- 0.10% ) [83.35%] > >>> 13,526,169,702 branches # 418.039 M/sec ( +- 0.10% ) [83.31%] > >>> 1,058,230 branch-misses # 0.01% of all branches ( +- 0.91% ) [83.36%] > >>> > >>> 32.413866442 seconds time elapsed ( +- 0.13% ) > >>> > >>>vhzp: > >>> Performance counter stats for './test_memcmp' (5 runs): > >>> > >>> 30327.183829 task-clock # 0.998 CPUs utilized ( +- 0.13% ) > >>> 38 context-switches # 0.001 K/sec ( +- 1.53% ) > >>> 0 CPU-migrations # 0.000 K/sec > >>> 4,218 page-faults # 0.139 K/sec ( +- 0.01% ) > >>> 71,964,773,660 cycles # 2.373 GHz ( +- 0.13% ) [83.35%] > >>> 31,191,284,231 stalled-cycles-frontend # 43.34% frontend cycles idle ( +- 0.40% ) [83.32%] > >>> 773,484,474 stalled-cycles-backend # 1.07% backend cycles idle ( +- 6.61% ) [66.67%] > >>> 134,982,215,437 instructions # 1.88 insns per cycle > >>> # 0.23 stalled cycles per insn ( +- 0.11% ) [83.32%] > >>> 13,509,150,683 branches # 445.447 M/sec ( +- 0.11% ) [83.34%] > >>> 1,017,667 branch-misses # 0.01% of all branches ( +- 1.07% ) [83.32%] > >>> > >>> 30.381324695 seconds time elapsed ( +- 0.13% ) > >>Could you tell me which data I should care in this performance > >>counter. And what's the benefit of your current implementation > >>compare to hpa's request? > > Sorry for my unintelligent. Could you tell me which data I should > care in this performance counter stats. The same question about the > second benchmark counter stats, thanks in adance. :-) I've missed relevant counters in this run, you can see them in the second benchmark. Relevant counters: L1-dcache-*, LLC-*: shows cache related stats (hits/misses); dTLB-*: shows data TLB hits and misses. Indirect relevant counters: stalled-cycles-*: how long CPU pipeline has to wait for data. > >>>Mirobenchmark2 > >>>============== > >>> > >>>test: > >>> posix_memalign((void **)&p, 2 * MB, 8 * GB); > >>> for (i = 0; i < 1000; i++) { > >>> char *_p = p; > >>> while (_p < p+4*GB) { > >>> assert(*_p == *(_p+4*GB)); > >>> _p += 4096; > >>> asm volatile ("": : :"memory"); > >>> } > >>> } > >>> > >>>hzp: > >>> Performance counter stats for 'taskset -c 0 ./test_memcmp2' (5 runs): > >>> > >>> 3505.727639 task-clock # 0.998 CPUs utilized ( +- 0.26% ) > >>> 9 context-switches # 0.003 K/sec ( +- 4.97% ) > >>> 4,384 page-faults # 0.001 M/sec ( +- 0.00% ) > >>> 8,318,482,466 cycles # 2.373 GHz ( +- 0.26% ) [33.31%] > >>> 5,134,318,786 stalled-cycles-frontend # 61.72% frontend cycles idle ( +- 0.42% ) [33.32%] > >>> 2,193,266,208 stalled-cycles-backend # 26.37% backend cycles idle ( +- 5.51% ) [33.33%] > >>> 9,494,670,537 instructions # 1.14 insns per cycle > >>> # 0.54 stalled cycles per insn ( +- 0.13% ) [41.68%] > >>> 2,108,522,738 branches # 601.451 M/sec ( +- 0.09% ) [41.68%] > >>> 158,746 branch-misses # 0.01% of all branches ( +- 1.60% ) [41.71%] > >>> 3,168,102,115 L1-dcache-loads > >>> # 903.693 M/sec ( +- 0.11% ) [41.70%] > >>> 1,048,710,998 L1-dcache-misses > >>> # 33.10% of all L1-dcache hits ( +- 0.11% ) [41.72%] > >>> 1,047,699,685 LLC-load > >>> # 298.854 M/sec ( +- 0.03% ) [33.38%] > >>> 2,287 LLC-misses > >>> # 0.00% of all LL-cache hits ( +- 8.27% ) [33.37%] > >>> 3,166,187,367 dTLB-loads > >>> # 903.147 M/sec ( +- 0.02% ) [33.35%] > >>> 4,266,538 dTLB-misses > >>> # 0.13% of all dTLB cache hits ( +- 0.03% ) [33.33%] > >>> > >>> 3.513339813 seconds time elapsed ( +- 0.26% ) > >>> > >>>vhzp: > >>> Performance counter stats for 'taskset -c 0 ./test_memcmp2' (5 runs): > >>> > >>> 27313.891128 task-clock # 0.998 CPUs utilized ( +- 0.24% ) > >>> 62 context-switches # 0.002 K/sec ( +- 0.61% ) > >>> 4,384 page-faults # 0.160 K/sec ( +- 0.01% ) > >>> 64,747,374,606 cycles # 2.370 GHz ( +- 0.24% ) [33.33%] > >>> 61,341,580,278 stalled-cycles-frontend # 94.74% frontend cycles idle ( +- 0.26% ) [33.33%] > >>> 56,702,237,511 stalled-cycles-backend # 87.57% backend cycles idle ( +- 0.07% ) [33.33%] > >>> 10,033,724,846 instructions # 0.15 insns per cycle > >>> # 6.11 stalled cycles per insn ( +- 0.09% ) [41.65%] > >>> 2,190,424,932 branches # 80.195 M/sec ( +- 0.12% ) [41.66%] > >>> 1,028,630 branch-misses # 0.05% of all branches ( +- 1.50% ) [41.66%] > >>> 3,302,006,540 L1-dcache-loads > >>> # 120.891 M/sec ( +- 0.11% ) [41.68%] > >>> 271,374,358 L1-dcache-misses > >>> # 8.22% of all L1-dcache hits ( +- 0.04% ) [41.66%] > >>> 20,385,476 LLC-load > >>> # 0.746 M/sec ( +- 1.64% ) [33.34%] > >>> 76,754 LLC-misses > >>> # 0.38% of all LL-cache hits ( +- 2.35% ) [33.34%] > >>> 3,309,927,290 dTLB-loads > >>> # 121.181 M/sec ( +- 0.03% ) [33.34%] > >>> 2,098,967,427 dTLB-misses > >>> # 63.41% of all dTLB cache hits ( +- 0.03% ) [33.34%] > >>> > >>> 27.364448741 seconds time elapsed ( +- 0.24% ) > >>For this case, the same question as above, thanks in adance. :-) > -- Kirill A. 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