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From: "adhemerval.zanella at linaro dot org" <sourceware-bugzilla@sourceware.org> To: glibc-bugs@sourceware.org Subject: [Bug string/30995] Zen 4: sub-optimal memcpy on very large copies Date: Mon, 30 Oct 2023 12:30:40 +0000 [thread overview] Message-ID: <bug-30995-131-5ztCbdsQUH@http.sourceware.org/bugzilla/> (raw) In-Reply-To: <bug-30995-131@http.sourceware.org/bugzilla/> https://sourceware.org/bugzilla/show_bug.cgi?id=30995 Adhemerval Zanella <adhemerval.zanella at linaro dot org> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |adhemerval.zanella at linaro dot o | |rg --- Comment #4 from Adhemerval Zanella <adhemerval.zanella at linaro dot org> --- On Zen3 I can confirm that REP MOSVB is not faster than the vectorized path, but with an unaligned destination the results are also subpar: # Default non-temporal stores $ ./memcpy_loop -f memcpy -D 1 4.19552 # GLIBC_TUNABLES=glibc.cpu.x86_non_temporal_threshold=134217730 $ ./memcpy_loop -f memcpy -D 1 11.7379 # Modified glibc with tunables to force REP MOVSB $ ./memcpy_loop -f memcpy -D 1 1.01945 With aligned stores I see ~20 GB on Zen3. I am even more convinced that REP MOVSB is not really a good strategy for Zen3. I still think it would be better to avoid non-temporal stores for unaligned inputs on Zen3. Another possibility would avoid unaligned stores, but it would require adding another code path that might not be optimal for all x86 cpus. -- You are receiving this mail because: You are on the CC list for the bug.
next prev parent reply other threads:[~2023-10-30 12:30 UTC|newest] Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top 2023-10-24 7:38 [Bug string/30995] New: " bmerry at sarao dot ac.za 2023-10-24 17:56 ` [Bug string/30995] " sam at gentoo dot org 2023-10-25 10:16 ` bmerry at sarao dot ac.za 2023-10-25 12:50 ` fweimer at redhat dot com 2023-10-25 13:21 ` bmerry at sarao dot ac.za 2023-10-30 12:30 ` adhemerval.zanella at linaro dot org [this message] 2023-10-30 12:34 ` adhemerval.zanella at linaro dot org 2023-10-30 14:00 ` bmerry at sarao dot ac.za 2023-10-30 14:24 ` bmerry at sarao dot ac.za 2023-10-30 16:17 ` adhemerval.zanella at linaro dot org 2023-11-07 13:01 ` jamborm at gcc dot gnu.org 2023-11-29 17:27 ` gabravier at gmail dot com 2023-11-29 17:30 ` sam at gentoo dot org 2023-11-29 21:08 ` pageexec at gmail dot com
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