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STOS is typically microcoded which can now be amortized over >> larger regions and the hint allows the hardware prefetcher to do a >> better job. >> >> Milan (EPYC 7J13, boost=0, preempt=full|lazy): >> >> mm/folio_zero_user x86/folio_zero_user change >> (GB/s +- stddev) (GB/s +- stddev) >> >> pg-sz=1GB 16.51 +- 0.54% 42.80 +- 3.48% + 159.2% >> pg-sz=2MB 11.89 +- 0.78% 16.12 +- 0.12% + 35.5% >> >> Icelakex (Platinum 8358, no_turbo=1, preempt=full|lazy): >> >> mm/folio_zero_user x86/folio_zero_user change >> (GB/s +- stddev) (GB/s +- stddev) >> >> pg-sz=1GB 8.01 +- 0.24% 11.26 +- 0.48% + 40.57% >> pg-sz=2MB 7.95 +- 0.30% 10.90 +- 0.26% + 37.10% > > How was this measured? Could you integrate this measurement as a new > tools/perf/bench/ subcommand so that people can try it on different > systems, etc.? There's already a 'perf bench mem' subcommand space > where this feature could be added to. This was a standalone trivial mmap workload similar to what qemu does when creating a VM, really any hugetlb mmap(). x86-64-stosq (lib/memset_64.S::__memset) should have the same performance characteristics but it uses malloc() for allocation. For this workload we want to control the allocation path as well. Let me see if it makes sense to extend perf bench mem memset to optionally allocate via mmap(MAP_HUGETLB) or add a new workload under perf bench mem which does that. Thanks for the review! -- ankur