Messages in this thread Patch in this message | | | Subject | Re: [PATCH] Athlon/Opteron Prefetch Fix for 2.6.0test5 + numbers | From | Dave Hansen <> | Date | 17 Sep 2003 00:15:20 -0700 |
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On Tue, 2003-09-16 at 22:08, Andrew Morton wrote: > But I would like to see some evidence that prefetch ever provides any > performance gain in-kernel. I spent some time fiddling a while back and > was unable to demonstrate any difference.
For SDET on the NUMA-Q, it's pretty small. Looks like well less than 1%. Mostly lost in the noise, though.
DISCLAIMER: SPEC(tm) and the benchmark name SDET(tm) are registered trademarks of the Standard Performance Evaluation Corporation. This benchmarking was performed for research purposes only, and the run results are non-compliant and not-comparable with any published results.
Prefetch on: Scripts | Average Throughput | Standard Deviation ----------+---------------------+--------------------- 16 | 15795.9100 | 711.3221 32 | 16450.5800 | 292.6028 64 | 15800.2400 | 126.2358
Prefetch off: Scripts | Average Throughput | Standard Deviation ----------+---------------------+--------------------- 16 | 15672.8600 | 438.5506 32 | 16376.4100 | 364.5610 64 | 15744.8100 | 208.9217
For those of you who care, I generated this with a neat little tool that some interns cooked up for us this summer. You hand it a little file like this and it throws back a wealth of information back at you. There's a central machine to which has a database of other machines and figures out the best fit for the job (can be more than 1 machine requested). In this case it's easy because there are very few 16x machines in the database. Oh, and like good interns, they stole a lot of code from Steve Pratt's "autobench".
class host num_cpus=16 +$mytest sdet "1 4 16 32 64" -l /tmp/sdet
disuseprofiler sar
# build the kernel with prefaulting off build stock 2.6.0-test5 \ -p http://elm3b114.beaverton.ibm.com/patches/prefetch-off.patch \ -m -j8 boot # sdet runs fast on ramfs fs -mountramfs /tmp/sdet run "sdet" $mytest setup umount /tmp/sdet
build stock 2.6.0-test5 -m -j8 boot fs -mountramfs /tmp/sdet run "sdet" $mytest setup umount /tmp/sdet
-- Dave Hansen haveblue@us.ibm.com --- include/asm/processor.h.orig Tue Sep 16 22:41:53 2003 +++ include/asm/processor.h Tue Sep 16 22:40:54 2003 @@ -571,34 +571,4 @@ #endif #define ASM_NOP_MAX 8 - -/* Prefetch instructions for Pentium III and AMD Athlon */ -/* It's not worth to care about 3dnow! prefetches for the K6 - because they are microcoded there and very slow. */ -#define ARCH_HAS_PREFETCH -extern inline void prefetch(const void *x) -{ - if (cpu_data[0].x86_vendor == X86_VENDOR_AMD) - return; /* Some athlons fault if the address is bad */ - alternative_input(ASM_NOP4, - "prefetchnta (%1)", - X86_FEATURE_XMM, - "r" (x)); -} - -#define ARCH_HAS_PREFETCH -#define ARCH_HAS_PREFETCHW -#define ARCH_HAS_SPINLOCK_PREFETCH - -/* 3dnow! prefetch to get an exclusive cache line. Useful for - spinlocks to avoid one state transition in the cache coherency protocol. */ -extern inline void prefetchw(const void *x) -{ - alternative_input(ASM_NOP4, - "prefetchw (%1)", - X86_FEATURE_3DNOW, - "r" (x)); -} -#define spin_lock_prefetch(x) prefetchw(x) - #endif /* __ASM_I386_PROCESSOR_H */ | |