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Date: Wed, 17 Dec 2008 00:59:00 +0100 From: Eric Dumazet <dada1@...mosbay.com> To: Rusty Russell <rusty@...tcorp.com.au> CC: David Miller <davem@...emloft.net>, rostedt@...dmis.org, akpm@...ux-foundation.org, linux-kernel@...r.kernel.org, mathieu.desnoyers@...ymtl.ca, paulus@...ba.org, benh@...nel.crashing.org, linux-ia64@...r.kernel.org, linux-s390@...r.kernel.org Subject: Re: local_add_return Rusty Russell a écrit : > On Tuesday 16 December 2008 17:43:14 David Miller wrote: >> Here ya go: > > Very interesting. There's a little noise there (that first local_inc of 243 > is wrong), but the picture is clear: trivalue is the best implementation for > sparc64. > > Note: trivalue uses 3 values, so instead of hitting random values across 8MB > it's across 24MB, and despite the resulting cache damage it's 15% faster. The > cpu_local_inc test is a single value, so no cache effects: it shows trivalue > to be 3 to 3.5 times faster in the cache-hot case. > > This sucks, because it really does mean that there's no one-size-fits-all > implementation of local_t. There's also no platform yet where atomic_long_t > is the right choice; and that's the default! > > Any chance of an IA64 or s390 run? You can normalize if you like, since > it's only to compare the different approaches. > > Cheers, > Rusty. > > Benchmarks for local_t variants > > (This patch also fixes the x86 cpu_local_* macros, which are obviously > unused). > > I chose a large array (1M longs) for the inc/add/add_return tests so > the trivalue case would show some cache pressure. > > The cpu_local_inc case is always cache-hot, so it's not comparable to > the others. Would be good to differenciate results, if data is already in cache or not... > > Time in ns per iteration (brackets is with CONFIG_PREEMPT=y): > > inc add add_return cpu_local_inc read > x86-32: 2.13 Ghz Core Duo 2 > atomic_long 118 118 115 17 17 really strange atomic_long performs so badly here. LOCK + data not in cache -> really really bad... > irqsave/rest 77 78 77 23 16 > trivalue 45 45 127 3(6) 21 > local_t 36 36 36 1(5) 17 > > x86-64: 2.6 GHz Dual-Core AMD Opteron 2218 > atomic_long 55 60 - 6 19 > irqsave/rest 54 54 - 11 19 > trivalue 47 47 - 5 28 > local_t 47 46 - 1 19 > Running local_t variant benchmarks atomic_long: local_inc=395001846/11 local_add=395000325/11 cpu_local_inc=362000295/10 local_read=49000040/1 local_add_return=396000322/11 (total was 1728053248) irqsave/restore: local_inc=498000400/14 local_add=496000395/14 cpu_local_inc=486000384/14 local_read=68000054/2 local_add_return=502000394/14 (total was 1728053248) trivalue: local_inc=1325001024/39 local_add=1324001226/39 cpu_local_inc=81000080/2 local_read=786000766/23 local_add_return=4193003781/124 (total was 1728053248) local_t: local_inc=69000059/2 local_add=69000058/2 cpu_local_inc=42000035/1 local_read=50000043/1 local_add_return=90000076/2 (total was 1728053248, warm_total 62914562) Intel(R) Xeon(R) CPU E5450 @ 3.00GHz two quadcore cpus, x86-32 kernel It seems Core2 are really better than Core Duo 2, or their cache is big enough to hold the array of your test... (at least for l1 & l2, their 4Mbytes working set fits in cache) processor : 7 vendor_id : GenuineIntel cpu family : 6 model : 23 model name : Intel(R) Xeon(R) CPU E5450 @ 3.00GHz stepping : 6 cpu MHz : 3000.099 cache size : 6144 KB <<<< yes, thats big :) >>>> If I double size of working set #define NUM_LOCAL_TEST (2*1024*1024) then I get quite different numbers : Running local_t variant benchmarks atomic_long: local_inc=6729007264/100 local_add=6727005943/100 cpu_local_inc=724000569/10 local_read=1030000784/15 local _add_return=6623004616/98 (total was 3456106496) irqsave/restore: local_inc=4458002796/66 local_add=4459001998/66 cpu_local_inc=971000381/14 local_read=1060000389/15 loc al_add_return=4528001388/67 (total was 3456106496) trivalue: local_inc=2871000855/42 local_add=2867000976/42 cpu_local_inc=162000052/2 local_read=1747000551/26 local_add_r eturn=8829002352/131 (total was 3456106496) local_t: local_inc=2210000492/32 local_add=2206000460/32 cpu_local_inc=84000017/1 local_read=1029000203/15 local_add_ret urn=2216000415/33 (total was 3456106496, warm_total 125829124) If now I reduce NUM_LOCAL_TEST to 256*1024 so that even trivalue l3 fits cache. Running local_t variant benchmarks atomic_long: local_inc=98984929/11 local_add=98984889/11 cpu_local_inc=89986248/10 local_read=11998165/1 local_add_retur n=99003292/11 (total was 2579496960) irqsave/restore: local_inc=124000102/14 local_add=124000102/14 cpu_local_inc=121000100/14 local_read=17000013/2 local_ad d_return=126000103/15 (total was 2579496960) trivalue: local_inc=21000017/2 local_add=20000016/2 cpu_local_inc=20000017/2 local_read=25000021/2 local_add_return=1360 00110/16 (total was 2579496960) local_t: local_inc=17000014/2 local_add=17000015/2 cpu_local_inc=11000009/1 local_read=12000010/1 local_add_return=23000 019/2 (total was 2579496960, warm_total 15728642) About trivalues, their use in percpu_counter local storage (one trivalue for each cpu) would make the accuracy a litle bit more lazy... -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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