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From: "goldstein.w.n at gmail dot com" <sourceware-bugzilla@sourceware.org> To: glibc-bugs@sourceware.org Subject: [Bug string/28354] New: For x86_64 string/memory functions use of EVEX registers sets HI16_ZMM_state adding context switch overhead Date: Mon, 20 Sep 2021 02:23:27 +0000 [thread overview] Message-ID: <bug-28354-131@http.sourceware.org/bugzilla/> (raw) https://sourceware.org/bugzilla/show_bug.cgi?id=28354 Bug ID: 28354 Summary: For x86_64 string/memory functions use of EVEX registers sets HI16_ZMM_state adding context switch overhead Product: glibc Version: 2.34 Status: UNCONFIRMED Severity: minor Priority: P2 Component: string Assignee: unassigned at sourceware dot org Reporter: goldstein.w.n at gmail dot com Target Milestone: --- Use of ymm16-ymm31 in the exex string/memory functions in sysdeps/x86_64/multtiarch sets HI16_ZMM_state to true. See: https://www.intel.com/content/dam/www/public/us/en/documents/manuals/64-ia-32-architectures-software-developer-vol-1-manual.pdf#page=321 This defeats the init optimization of various xsave* context switching instructions. Overall it adds at the very least 1024 bytes to context switches. Simple reproduction: ``` .global _start .text _start: vpxorq %ymm16, %ymm16, %ymm16 vzeroupper loop: jmp loop movl $60, %eax xorl %edi, %edi syscall ``` Then check: cat /proc/${pid}/arch_status Which will show the state being continuously updated. State is updated during context switch here: https://elixir.bootlin.com/linux/v5.15-rc1/source/arch/x86/kernel/fpu/core.c#L108) -- You are receiving this mail because: You are on the CC list for the bug.
next reply other threads:[~2021-09-20 2:23 UTC|newest] Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-09-20 2:23 goldstein.w.n at gmail dot com [this message] 2021-09-20 2:28 ` [Bug string/28354] " goldstein.w.n at gmail dot com 2021-09-20 14:09 ` hjl.tools at gmail dot com 2021-09-22 21:10 ` goldstein.w.n at gmail dot com
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