2017-08-21 16:07:18 +02:00
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From 799859f6635d68487ea2472bd79d96a7639a1ab1 Mon Sep 17 00:00:00 2001
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From: "H.J. Lu" <hjl.tools@gmail.com>
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Date: Sun, 6 Aug 2017 10:44:30 -0700
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Subject: [PATCH 04] x86-64: Use _dl_runtime_resolve_opt only with AVX512F
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[BZ #21871]
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On AVX machines with XGETBV (ECX == 1) like Skylake processors,
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(gdb) disass _dl_runtime_resolve_avx_opt
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Dump of assembler code for function _dl_runtime_resolve_avx_opt:
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0x0000000000015890 <+0>: push %rax
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0x0000000000015891 <+1>: push %rcx
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0x0000000000015892 <+2>: push %rdx
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0x0000000000015893 <+3>: mov $0x1,%ecx
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0x0000000000015898 <+8>: xgetbv
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0x000000000001589b <+11>: mov %eax,%r11d
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0x000000000001589e <+14>: pop %rdx
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0x000000000001589f <+15>: pop %rcx
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0x00000000000158a0 <+16>: pop %rax
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0x00000000000158a1 <+17>: and $0x4,%r11d
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0x00000000000158a5 <+21>: bnd je 0x16200 <_dl_runtime_resolve_sse_vex>
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End of assembler dump.
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is slower than:
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(gdb) disass _dl_runtime_resolve_avx_slow
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Dump of assembler code for function _dl_runtime_resolve_avx_slow:
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0x0000000000015850 <+0>: vorpd %ymm0,%ymm1,%ymm8
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0x0000000000015854 <+4>: vorpd %ymm2,%ymm3,%ymm9
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0x0000000000015858 <+8>: vorpd %ymm4,%ymm5,%ymm10
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0x000000000001585c <+12>: vorpd %ymm6,%ymm7,%ymm11
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0x0000000000015860 <+16>: vorpd %ymm8,%ymm9,%ymm9
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0x0000000000015865 <+21>: vorpd %ymm10,%ymm11,%ymm10
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0x000000000001586a <+26>: vpcmpeqd %xmm8,%xmm8,%xmm8
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0x000000000001586f <+31>: vorpd %ymm9,%ymm10,%ymm10
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0x0000000000015874 <+36>: vptest %ymm10,%ymm8
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0x0000000000015879 <+41>: bnd jae 0x158b0 <_dl_runtime_resolve_avx>
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0x000000000001587c <+44>: vzeroupper
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0x000000000001587f <+47>: bnd jmpq 0x16200 <_dl_runtime_resolve_sse_vex>
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End of assembler dump.
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(gdb)
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since xgetbv takes much more cycles than single cycle operations like
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vpord/vvpcmpeq/ptest. _dl_runtime_resolve_opt should be used only with
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AVX512 where AVX512 instructions lead to lower CPU frequency on Skylake
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server.
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[BZ #21871]
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* sysdeps/x86/cpu-features.c (init_cpu_features): Set
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bit_arch_Use_dl_runtime_resolve_opt only with AVX512F.
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(cherry picked from commit d2cf37c0a2a375cf2fde69f1afbcc49e45368fc4)
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---
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ChangeLog | 6 ++++++
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sysdeps/x86/cpu-features.c | 7 +++++--
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2 files changed, 11 insertions(+), 2 deletions(-)
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diff --git a/ChangeLog b/ChangeLog
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2017-10-10 16:38:13 +02:00
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index 4357ad1eb8..764c827161 100644
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2017-08-21 16:07:18 +02:00
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--- a/ChangeLog
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+++ b/ChangeLog
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@@ -1,3 +1,9 @@
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+2017-08-06 H.J. Lu <hongjiu.lu@intel.com>
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+
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+ [BZ #21871]
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+ * sysdeps/x86/cpu-features.c (init_cpu_features): Set
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+ bit_arch_Use_dl_runtime_resolve_opt only with AVX512F.
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+
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2017-08-03 Aurelien Jarno <aurelien@aurel32.net>
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* stdlib/getentropy.c (getentropy): Change return type to int.
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diff --git a/sysdeps/x86/cpu-features.c b/sysdeps/x86/cpu-features.c
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2017-10-10 16:38:13 +02:00
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index 1d087ea732..6f900840d4 100644
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2017-08-21 16:07:18 +02:00
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--- a/sysdeps/x86/cpu-features.c
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+++ b/sysdeps/x86/cpu-features.c
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@@ -244,10 +244,13 @@ init_cpu_features (struct cpu_features *cpu_features)
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|= bit_arch_Prefer_No_AVX512;
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/* To avoid SSE transition penalty, use _dl_runtime_resolve_slow.
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- If XGETBV suports ECX == 1, use _dl_runtime_resolve_opt. */
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+ If XGETBV suports ECX == 1, use _dl_runtime_resolve_opt.
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+ Use _dl_runtime_resolve_opt only with AVX512F since it is
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+ slower than _dl_runtime_resolve_slow with AVX. */
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cpu_features->feature[index_arch_Use_dl_runtime_resolve_slow]
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|= bit_arch_Use_dl_runtime_resolve_slow;
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- if (cpu_features->max_cpuid >= 0xd)
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+ if (CPU_FEATURES_ARCH_P (cpu_features, AVX512F_Usable)
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+ && cpu_features->max_cpuid >= 0xd)
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{
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unsigned int eax;
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