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authorH.J. Lu <hjl.tools@gmail.com>2017-08-04 11:14:19 -0700
committerH.J. Lu <hjl.tools@gmail.com>2017-08-04 11:14:33 -0700
commitd2cf37c0a2a375cf2fde69f1afbcc49e45368fc4 (patch)
tree9de1e2154736c6c3c7990e2279b8ab6b02f714e2 /sysdeps
parentc8a0e6ec03b2646842fe3c7c59955f55175f3669 (diff)
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x86-64: Use _dl_runtime_resolve_opt only with AVX512F [BZ #21871]
On AVX machines with XGETBV (ECX == 1) like Skylake processors, (gdb) disass _dl_runtime_resolve_avx_opt Dump of assembler code for function _dl_runtime_resolve_avx_opt: 0x0000000000015890 <+0>: push %rax 0x0000000000015891 <+1>: push %rcx 0x0000000000015892 <+2>: push %rdx 0x0000000000015893 <+3>: mov $0x1,%ecx 0x0000000000015898 <+8>: xgetbv 0x000000000001589b <+11>: mov %eax,%r11d 0x000000000001589e <+14>: pop %rdx 0x000000000001589f <+15>: pop %rcx 0x00000000000158a0 <+16>: pop %rax 0x00000000000158a1 <+17>: and $0x4,%r11d 0x00000000000158a5 <+21>: bnd je 0x16200 <_dl_runtime_resolve_sse_vex> End of assembler dump. is slower than: (gdb) disass _dl_runtime_resolve_avx_slow Dump of assembler code for function _dl_runtime_resolve_avx_slow: 0x0000000000015850 <+0>: vorpd %ymm0,%ymm1,%ymm8 0x0000000000015854 <+4>: vorpd %ymm2,%ymm3,%ymm9 0x0000000000015858 <+8>: vorpd %ymm4,%ymm5,%ymm10 0x000000000001585c <+12>: vorpd %ymm6,%ymm7,%ymm11 0x0000000000015860 <+16>: vorpd %ymm8,%ymm9,%ymm9 0x0000000000015865 <+21>: vorpd %ymm10,%ymm11,%ymm10 0x000000000001586a <+26>: vpcmpeqd %xmm8,%xmm8,%xmm8 0x000000000001586f <+31>: vorpd %ymm9,%ymm10,%ymm10 0x0000000000015874 <+36>: vptest %ymm10,%ymm8 0x0000000000015879 <+41>: bnd jae 0x158b0 <_dl_runtime_resolve_avx> 0x000000000001587c <+44>: vzeroupper 0x000000000001587f <+47>: bnd jmpq 0x16200 <_dl_runtime_resolve_sse_vex> End of assembler dump. (gdb) since xgetbv takes much more cycles than single cycle operations like vpord/vvpcmpeq/ptest. _dl_runtime_resolve_opt should be used only with AVX512 where AVX512 instructions lead to lower CPU frequency on Skylake server. [BZ #21871] * sysdeps/x86/cpu-features.c (init_cpu_features): Set bit_arch_Use_dl_runtime_resolve_opt only with AVX512F.
Diffstat (limited to 'sysdeps')
-rw-r--r--sysdeps/x86/cpu-features.c7
1 files changed, 5 insertions, 2 deletions
diff --git a/sysdeps/x86/cpu-features.c b/sysdeps/x86/cpu-features.c
index 1d087ea..6f90084 100644
--- a/sysdeps/x86/cpu-features.c
+++ b/sysdeps/x86/cpu-features.c
@@ -244,10 +244,13 @@ init_cpu_features (struct cpu_features *cpu_features)
|= bit_arch_Prefer_No_AVX512;
/* To avoid SSE transition penalty, use _dl_runtime_resolve_slow.
- If XGETBV suports ECX == 1, use _dl_runtime_resolve_opt. */
+ If XGETBV suports ECX == 1, use _dl_runtime_resolve_opt.
+ Use _dl_runtime_resolve_opt only with AVX512F since it is
+ slower than _dl_runtime_resolve_slow with AVX. */
cpu_features->feature[index_arch_Use_dl_runtime_resolve_slow]
|= bit_arch_Use_dl_runtime_resolve_slow;
- if (cpu_features->max_cpuid >= 0xd)
+ if (CPU_FEATURES_ARCH_P (cpu_features, AVX512F_Usable)
+ && cpu_features->max_cpuid >= 0xd)
{
unsigned int eax;