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Message-ID: <20131107212341.GA9709@hmsreliant.think-freely.org> Date: Thu, 7 Nov 2013 16:23:41 -0500 From: Neil Horman <nhorman@...driver.com> To: Andi Kleen <andi@...stfloor.org> Cc: linux-kernel@...r.kernel.org, sebastien.dugue@...l.net, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org, netdev@...r.kernel.org Subject: Re: [PATCH v2 2/2] x86: add prefetching to do_csum On Wed, Nov 06, 2013 at 12:19:52PM -0800, Andi Kleen wrote: > Neil Horman <nhorman@...driver.com> writes: > > > do_csum was identified via perf recently as a hot spot when doing > > receive on ip over infiniband workloads. After alot of testing and > > ideas, we found the best optimization available to us currently is to > > prefetch the entire data buffer prior to doing the checksum > > On what CPU? Most modern CPUs should not have any trouble at all > prefetching a linear access. > > Also for large buffers it is unlikely that all the prefetches > are actually executed, there is usually some limit. > > As a minimum you would need: > - run it with a range of buffer sizes > - run this on a range of different CPUs and show no major regressions > - describe all of this actually in the description > > But I find at least this patch very dubious. > > -Andi > Well, if you look back in the thread, you can see several tests done with various forms of prefetching, that show performance improvements, but if you want them all collected, heres what I have, using the perf bench from patch 1. As you can see, you're right, on newer hardware theres negligible advantage (but no regression that I can see). On older hardware however, we see a definate improvement (up to 3%). I'm afraid I don't have a wide variety of hardware handy at the moment to do any large scale testing on multiple cpu's. But if you have them available, please share your results Regards Neil vendor_id : AuthenticAMD cpu family : 16 model : 8 model name : AMD Opteron(tm) Processor 4130 stepping : 0 microcode : 0x10000da cpu MHz : 800.000 cache size : 512 KB physical id : 1 siblings : 4 core id : 3 cpu cores : 4 apicid : 11 initial apicid : 11 fpu : yes fpu_exception : yes cpuid level : 5 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt pdpe1gb rdtscp lm 3dnowext 3dnow constant_tsc rep_good nopl nonstop_tsc extd_apicid pni monitor cx16 popcnt lahf_lm cmp_legacy svm extapic cr8_legacy abm sse4a misalignsse 3dnowprefetch osvw ibs skinit wdt nodeid_msr hw_pstate npt lbrv svm_lock nrip_save pausefilter bogomips : 5200.49 TLB size : 1024 4K pages clflush size : 64 cache_alignment : 64 address sizes : 48 bits physical, 48 bits virtual power management: ts ttp tm stc 100mhzsteps hwpstate Without prefecth: length | Set Sz| iterations | cycles/byte 1500B | 64MB | 1000000 | 1.432338 1500B | 128MB | 1000000 | 1.426212 1500B | 256MB | 1000000 | 1.425988 1500B | 512MB | 1000000 | 1.517873 9000B | 64MB | 1000000 | 0.897998 9000B | 128MB | 1000000 | 0.884120 9000B | 256MB | 1000000 | 0.881770 9000B | 512MB | 1000000 | 0.883644 64KB | 64MB | 1000000 | 0.813054 64KB | 128MB | 1000000 | 0.801859 64KB | 256MB | 1000000 | 0.796415 64KB | 512MB | 1000000 | 0.793869 With prefetch: length | Set Sz| iterations | cycles/byte 1500B | 64MB | 1000000 | 1.442855 1500B | 128MB | 1000000 | 1.438841 1500B | 256MB | 1000000 | 1.427324 1500B | 512MB | 1000000 | 1.462715 9000B | 64MB | 1000000 | 0.894097 9000B | 128MB | 1000000 | 0.884738 9000B | 256MB | 1000000 | 0.881370 9000B | 512MB | 1000000 | 0.884799 64KB | 64MB | 1000000 | 0.813512 64KB | 128MB | 1000000 | 0.801596 64KB | 256MB | 1000000 | 0.795575 64KB | 512MB | 1000000 | 0.793927 ========================================================================================== vendor_id : GenuineIntel cpu family : 6 model : 42 model name : Intel(R) Core(TM) i7-2600 CPU @ 3.40GHz stepping : 7 microcode : 0x29 cpu MHz : 2754.000 cache size : 8192 KB physical id : 0 siblings : 8 core id : 3 cpu cores : 4 apicid : 7 initial apicid : 7 fpu : yes fpu_exception : yes cpuid level : 13 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf eagerfpu pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 cx16 xtpr pdcm pcid sse4_1 sse4_2 x2apic popcnt tsc_deadline_timer aes xsave avx lahf_lm ida arat epb xsaveopt pln pts dtherm tpr_shadow vnmi flexpriority ept vpid bogomips : 6784.46 clflush size : 64 cache_alignment : 64 address sizes : 36 bits physical, 48 bits virtual Without prefetch: length | Set Sz| iterations | cycles/byte 1500B | 64MB | 1000000 | 1.343645 1500B | 128MB | 1000000 | 1.345782 1500B | 256MB | 1000000 | 1.353145 1500B | 512MB | 1000000 | 1.354844 9000B | 64MB | 1000000 | 0.856552 9000B | 128MB | 1000000 | 0.852786 9000B | 256MB | 1000000 | 0.854705 9000B | 512MB | 1000000 | 0.863308 64KB | 64MB | 1000000 | 0.771888 64KB | 128MB | 1000000 | 0.773453 64KB | 256MB | 1000000 | 0.771728 64KB | 512MB | 1000000 | 0.771390 With prefetching: length | Set Sz| iterations | cycles/byte 1500B | 64MB | 1000000 | 1.344733 1500B | 128MB | 1000000 | 1.342285 1500B | 256MB | 1000000 | 1.344818 1500B | 512MB | 1000000 | 1.342632 9000B | 64MB | 1000000 | 0.851043 9000B | 128MB | 1000000 | 0.850629 9000B | 256MB | 1000000 | 0.852207 9000B | 512MB | 1000000 | 0.851927 64KB | 64MB | 1000000 | 0.768549 64KB | 128MB | 1000000 | 0.768623 64KB | 256MB | 1000000 | 0.768938 64KB | 512MB | 1000000 | 0.768824 ========================================================================================== vendor_id : AuthenticAMD cpu family : 16 model : 9 model name : AMD Opteron(tm) Processor 6172 stepping : 1 microcode : 0x10000d9 cpu MHz : 800.000 cache size : 512 KB physical id : 1 siblings : 12 core id : 5 cpu cores : 12 apicid : 43 initial apicid : 27 fpu : yes fpu_exception : yes cpuid level : 5 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt pdpe1gb rdtscp lm 3dnowext 3dnow constant_tsc rep_good nopl nonstop_tsc extd_apicid amd_dcm pni monitor cx16 popcnt lahf_lm cmp_legacy svm extapic cr8_legacy abm sse4a misalignsse 3dnowprefetch osvw ibs skinit wdt nodeid_msr hw_pstate npt lbrv svm_lock nrip_save pausefilter bogomips : 4189.63 TLB size : 1024 4K pages clflush size : 64 cache_alignment : 64 address sizes : 48 bits physical, 48 bits virtual power management: ts ttp tm stc 100mhzsteps hwpstate Without prefetch: length | Set Sz| iterations | cycles/byte 1500B | 64MB | 1000000 | 1.415370 1500B | 128MB | 1000000 | 1.437025 1500B | 256MB | 1000000 | 1.424822 1500B | 512MB | 1000000 | 1.442021 9000B | 64MB | 1000000 | 0.891699 9000B | 128MB | 1000000 | 0.884261 9000B | 256MB | 1000000 | 0.880179 9000B | 512MB | 1000000 | 0.882190 64KB | 64MB | 1000000 | 0.813047 64KB | 128MB | 1000000 | 0.800755 64KB | 256MB | 1000000 | 0.795207 64KB | 512MB | 1000000 | 0.792065 With prefetch: length | Set Sz| iterations | cycles/byte 1500B | 64MB | 1000000 | 1.424003 1500B | 128MB | 1000000 | 1.435567 1500B | 256MB | 1000000 | 1.446858 1500B | 512MB | 1000000 | 1.459407 9000B | 64MB | 1000000 | 0.899858 9000B | 128MB | 1000000 | 0.885170 9000B | 256MB | 1000000 | 0.883936 9000B | 512MB | 1000000 | 0.886158 64KB | 64MB | 1000000 | 0.814136 64KB | 128MB | 1000000 | 0.802202 64KB | 256MB | 1000000 | 0.796140 64KB | 512MB | 1000000 | 0.793792 ========================================================================================== processor : 0 vendor_id : AuthenticAMD cpu family : 6 model : 10 model name : AMD Athlon(tm) XP 2800+ stepping : 0 cpu MHz : 2079.461 cache size : 512 KB fdiv_bug : no f00f_bug : no coma_bug : no fpu : yes fpu_exception : yes cpuid level : 1 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 mmx fxsr sse syscall mmxext 3dnowext 3dnow bogomips : 4158.92 clflush size : 32 cache_alignment : 32 address sizes : 34 bits physical, 32 bits virtual power management: ts Without prefetch: length | Set Sz| iterations | cycles/byte 1500B | 64MB | 1000000 | 3.335217 1500B | 128MB | 1000000 | 3.403103 1500B | 256MB | 1000000 | 3.445059 1500B | 512MB | 1000000 | 3.742008 9000B | 64MB | 1000000 | 47.466255 9000B | 128MB | 1000000 | 47.742751 9000B | 256MB | 1000000 | 47.965001 9000B | 512MB | 1000000 | 48.589349 64KB | 64MB | 1000000 | 118.088638 64KB | 128MB | 1000000 | 118.261744 64KB | 256MB | 1000000 | 118.349641 64KB | 512MB | 1000000 | 118.695321 With prefetch: length | Set Sz| iterations | cycles/byte 1500B | 64MB | 1000000 | 3.231086 1500B | 128MB | 1000000 | 3.423485 1500B | 256MB | 1000000 | 3.278899 1500B | 512MB | 1000000 | 3.545504 9000B | 64MB | 1000000 | 46.907795 9000B | 128MB | 1000000 | 47.321743 9000B | 256MB | 1000000 | 47.306189 9000B | 512MB | 1000000 | 48.144320 64KB | 64MB | 1000000 | 117.897735 64KB | 128MB | 1000000 | 118.122266 64KB | 256MB | 1000000 | 118.126397 64KB | 512MB | 1000000 | 118.546901 -- 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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