On Fri, Aug 8, 2025 at 2:21 PM Alan Kelly <alanke...@google.com> wrote:
> 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
>
https://www.intel.com/content/www/us/en/developer/articles/technical/software-security-guidance/technical-documentation/gather-data-sampling.html
Broadwell:
hscale_8_to_15__fs_4_dstW_512_c: 3379.5 ( 1.00x)
hscale_8_to_15__fs_4_dstW_512_sse2: 615.7 ( 5.49x)
hscale_8_to_15__fs_4_dstW_512_ssse3: 613.4 ( 5.51x)
hscale_8_to_15__fs_4_dstW_512_avx2: 495.7 ( 6.82x)
Skylake:
hscale_8_to_15__fs_4_dstW_512_c: 3411.4 ( 1.00x)
hscale_8_to_15__fs_4_dstW_512_sse2: 591.0 ( 5.77x)
hscale_8_to_15__fs_4_dstW_512_ssse3: 591.5 ( 5.77x)
hscale_8_to_15__fs_4_dstW_512_avx2: 1386.2 ( 2.46x)
Cascade Lake:
hscale_8_to_15__fs_4_dstW_512_c: 3231.3 ( 1.00x)
hscale_8_to_15__fs_4_dstW_512_sse2: 517.9 ( 6.24x)
hscale_8_to_15__fs_4_dstW_512_ssse3: 521.6 ( 6.19x)
hscale_8_to_15__fs_4_dstW_512_avx2: 1775.0 ( 1.82x)
Sapphire Rapids:
hscale_8_to_15__fs_4_dstW_512_c: 1840.0 ( 1.00x)
hscale_8_to_15__fs_4_dstW_512_sse2: 287.9 ( 6.39x)
hscale_8_to_15__fs_4_dstW_512_ssse3: 293.8 ( 6.26x)
hscale_8_to_15__fs_4_dstW_512_avx2: 219.2 ( 8.40x)
_______________________________________________
ffmpeg-devel mailing list
ffmpeg-devel@ffmpeg.org
https://ffmpeg.org/mailman/listinfo/ffmpeg-devel
To unsubscribe, visit link above, or email
ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
