Intel provided a microcode update to mitigate this security
vulnerability which has a huge negative performance impact on gather
instructions. This means that hscale 8to15 avx2, which uses gather
extensively, is no longer faster than SSSE3 on impacted CPUs.
---
libavutil/x86/cpu.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/libavutil/x86/cpu.c b/libavutil/x86/cpu.c
index d6cd4fab9c..923c63e0c4 100644
--- a/libavutil/x86/cpu.c
+++ b/libavutil/x86/cpu.c
@@ -244,9 +244,11 @@ int ff_get_cpu_flags_x86(void)
family == 6 && model < 23)
rval |= AV_CPU_FLAG_SSSE3SLOW;
- /* Haswell has slow gather */
- if ((rval & AV_CPU_FLAG_AVX2) && family == 6 && model < 70)
+ /* Ice Lake and below have slow gather due to Gather Data Sampling
+ * mitigation. */
+ if ((rval & AV_CPU_FLAG_AVX2) && family == 6 && model < 143) {
rval |= AV_CPU_FLAG_SLOW_GATHER;
+ }
}
#endif /* cpuid */
--
2.50.1.703.g449372360f-goog
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