Messages in this thread | | | Date | Fri, 17 Nov 2023 17:09:40 +0100 | From | Borislav Petkov <> | Subject | Re: [linus:master] [iov_iter] c9eec08bac: vm-scalability.throughput -16.9% regression |
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On Fri, Nov 17, 2023 at 02:12:17PM +0000, David Howells wrote: > Borislav Petkov <bp@alien8.de> wrote: > > > Hmm, stupid question: are those results better than without that > > oneliner? > > Without any changes, I see something like: > > iov_kunit_benchmark_bvec: avg 3185 uS, stddev 19 uS > iov_kunit_benchmark_bvec: avg 3186 uS, stddev 9 uS > iov_kunit_benchmark_bvec: avg 3244 uS, stddev 153 uS > iov_kunit_benchmark_bvec_split: avg 3397 uS, stddev 16 uS > iov_kunit_benchmark_bvec_split: avg 3400 uS, stddev 16 uS > iov_kunit_benchmark_bvec_split: avg 3402 uS, stddev 34 uS > iov_kunit_benchmark_kvec: avg 2818 uS, stddev 550 uS > iov_kunit_benchmark_kvec: avg 2906 uS, stddev 21 uS > iov_kunit_benchmark_kvec: avg 2923 uS, stddev 1496 uS > iov_kunit_benchmark_xarray: avg 3564 uS, stddev 6 uS > iov_kunit_benchmark_xarray: avg 3573 uS, stddev 17 uS > iov_kunit_benchmark_xarray: avg 3575 uS, stddev 58 uS > iov_kunit_benchmark_xarray_to_bvec: avg 3929 uS, stddev 9 uS > iov_kunit_benchmark_xarray_to_bvec: avg 3930 uS, stddev 6 uS > iov_kunit_benchmark_xarray_to_bvec: avg 3930 uS, stddev 7 uS
Which looks like those added memcpy calls add a lot of overhead due to the mitigations crap.
You could verify that if you boot a kernel with the oneliner but add "mitigations=off" on the cmdline.
Or profile the workload and check whether the return thunks appear higher in the profile... I'd say.
Thx.
-- Regards/Gruss, Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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