Messages in this thread | | | Subject | RE: [patch 10/10] Scheduler profiling - Use immediate values | Date | Fri, 6 Jul 2007 13:57:03 -0700 | From | "Li, Tong N" <> |
| |
> I found that memory latency is difficult to measure in modern x86 > CPUs because they have very clever prefetchers that can often > outwit benchmarks.
A pointer-chasing program that accesses a random sequence of addresses usually can produce a good estimate on memory latency. Also, prefetching can be turned off in BIOS or by modifying the MSRs.
> Another trap on P4 is that RDTSC is actually quite slow and synchronizes > the CPU; that can add large measurement errors. > > -Andi
The cost can be amortized if the portion of memory accesses is long enough.
tong - 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/
| |