Messages in this thread | | | From | Linus Torvalds <> | Date | Thu, 16 Nov 2023 17:36:47 -0500 | Subject | Re: [linus:master] [iov_iter] c9eec08bac: vm-scalability.throughput -16.9% regression |
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On Thu, 16 Nov 2023 at 16:13, David Howells <dhowells@redhat.com> wrote: > > > Okay, I disabled RETPOLINE, which seems like it should be the important one. > With inlined memcpy:
Yeah, your machine really seems to hate the out-of-line call version.
It is also not unlikely that the benchmark is the perfect example of that kind of "bad memory copy benchmark" where the actual results of the copy are never used or touched. It's one case that sometimes makes "rep movs" look (somewhat artificially) good, just because the optimized rep string will do cacheline copies in L2. So if you never touch the source or the destination of the copy, it never even gets brought into the L1.
Linus
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