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Intel leads in AVX/AVX2/AVX512 perf by a large factor over Ryzen CPUs. (A software that makes that manifest is Prime95 (Mersenne primality tester)). Looks like

by mpreda 8y ago

Intel leads in AVX/AVX2/AVX512 perf by a large factor over Ryzen CPUs. (A software that makes that manifest is Prime95 (Mersenne primality tester)). Looks like AMD did have to cut something after all.

bitL 8y ago
Yeah, it was known Ryzen cut AVX performance in order to lower power consumption. That's how we ended up with 65W 8-core at 14nm.
sliken 8y ago
Indeed, but the problem is that often AVX intensive code triggers intel to significantly throttle, or run out of bandwidth from cache or main memory. A surprisingly number of codes don't seem to benefit from the AVX performance. Most notably even on the most FP intensive code don't seem to benefit much from the higher end xeons (with two AVX512 units) over the lower models with a single AVX512 unit. So sure if you compute mercenne primes all day go for it. If you are actually doing some real world work that's vector intensive you are often better off with AMD (per $.) Keep in mind that today's chips have more performance per memory bandwidth then previous generations. So generally memory is a bigger bottleneck and AMD's 1.33x advantage in bandwidth/memory channels is an advantage on a wider variety of codes than the previous generation.
- paulmd 8y ago
  > Indeed, but the problem is that often AVX intensive code triggers intel to significantly throttle Xeon-W, HEDT, and consumer processors suffer this to a much smaller extent than Skylake-SP does, and this slowdown is already baked into the benchmarks (the deviation from benchmarks only really exists for mixed workloads). In most cases, AVX is still a huge speedup. Also, on consumer+HEDT you can manually configure the AVX offset anyway. Want zero offset, and can handle the power/heat? Go hog wild... > Most notably even on the most FP intensive code don't seem to benefit much from the higher end xeons (with two AVX512 units) over the lower models with a single AVX512 unit. Intel's documentation on some of the HEDT chips was incorrect, the i7s actually have dual AVX512 as well as the i9s. If you were referring to HEDT as "Xeons" that would be why. Otherwise, it might be another documentation issue. The difference should be very clear in something like x265 encoding.

by mpreda 8y ago

bitL 8y ago

Yeah, it was known Ryzen cut AVX performance in order to lower power consumption. That's how we ended up with 65W 8-core at 14nm.

sliken 8y ago

Indeed, but the problem is that often AVX intensive code triggers intel to significantly throttle, or run out of bandwidth from cache or main memory. A surprisingly number of codes don't seem to benefit from the AVX performance. Most notably even on the most FP intensive code don't seem to benefit much from the higher end xeons (with two AVX512 units) over the lower models with a single AVX512 unit. So sure if you compute mercenne primes all day go for it. If you are actually doing some real world work that's vector intensive you are often better off with AMD (per $.) Keep in mind that today's chips have more performance per memory bandwidth then previous generations. So generally memory is a bigger bottleneck and AMD's 1.33x advantage in bandwidth/memory channels is an advantage on a wider variety of codes than the previous generation.

paulmd 8y ago
> Indeed, but the problem is that often AVX intensive code triggers intel to significantly throttle Xeon-W, HEDT, and consumer processors suffer this to a much smaller extent than Skylake-SP does, and this slowdown is already baked into the benchmarks (the deviation from benchmarks only really exists for mixed workloads). In most cases, AVX is still a huge speedup. Also, on consumer+HEDT you can manually configure the AVX offset anyway. Want zero offset, and can handle the power/heat? Go hog wild... > Most notably even on the most FP intensive code don't seem to benefit much from the higher end xeons (with two AVX512 units) over the lower models with a single AVX512 unit. Intel's documentation on some of the HEDT chips was incorrect, the i7s actually have dual AVX512 as well as the i9s. If you were referring to HEDT as "Xeons" that would be why. Otherwise, it might be another documentation issue. The difference should be very clear in something like x265 encoding.