Messages in this thread |  | | Date | Sat, 2 Apr 2022 16:50:05 +0800 | From | Feng Tang <> | Subject | Re: [NUMA Balancing] e39bb6be9f: will-it-scale.per_thread_ops 64.4% improvement |
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Hi Linus,
On Fri, Apr 01, 2022 at 09:35:24AM -0700, Linus Torvalds wrote: > On Fri, Apr 1, 2022 at 2:42 AM kernel test robot <oliver.sang@intel.com> wrote: > > > > FYI, we noticed a 64.4% improvement of will-it-scale.per_thread_ops due to commit: > > e39bb6be9f2b ("NUMA Balancing: add page promotion counter") > > That looks odd and unlikely. > > That commit only modifies some page counting statistics. Sure, it > could be another cache layout thing, and maybe it's due to the subtle > change in how NUMA_PAGE_MIGRATE gets counted, but it still looks a bit > odd.
We did a quick check about cache stuff by disabling HW cache prefetch completely (writing 0xf to MSR 0x1a4), and the performance change is almost gone:
ee97347fe058d020 e39bb6be9f2b39a6dbaeff48436 ---------------- --------------------------- 134793 -1.4% 132867 will-it-scale.per_thread_ops
The test box is a Cascadelake machine with 4 nodes, and the similar trend is found on a 2 nodes machine, that the commit has 55% improvement with HW cache prefetch enabled, and has less than 1% change when disabled.
Though we still cannot pin-point the exact place affected.
Also per our experience, the patch changing vm statistics can easily trigger strange performance bumps for micro-benchmarks like will-it-scale, stress-ng etc.
Thanks, Feng
> Linus
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