3 ms·
Check out the "Intel AVX Instructions Optimization" slide on http://anandtech.com/show/10158/the-intel-xeon-e5-v4-review/3 http://anandtech.com/show/10158/the-i
by knweiss 11y ago
Check out the "Intel AVX Instructions Optimization" slide on
http://anandtech.com/show/10158/the-intel-xeon-e5-v4-review/3 http://anandtech.com/show/10158/the-intel-xeon-e5-v4-review/....
Quote:
On Haswell, one AVX instruction on one core forced all cores on the same socket to slow down their clockspeed by around 2 to 4 speed bins (-200,-400 MHz) for at least 1 ms, as AVX has a higher power requirement that reduces how much a CPU can turbo. On Broadwell, only the cores that run AVX code will be reducing their clockspeed, allowing the other cores to run at higher speeds.
- tveita 11y agoInteresting, that seems to contradict the information in http://www.intel.com/content/dam/www/public/us/en/documents/white-papers/performance-xeon-e5-v3-advanced-vector-extensions-paper.pdf http://www.intel.com/content/dam/www/public/us/en/documents/... Specifically, the FAQ says: "Will running a small number of Intel AVX instructions reduce frequency below the regular marked frequency? No, frequency will be reduced below the regular marked frequency only if a real power or thermal constraint is reached, not just due to the presence of Intel AVX instructions. Some workloads that utilize Intel AVX instructions could still achieve turbo above the marked TDP frequency."
- semi-extrinsic 11y agoNo, you're actually agreeing: GP says "it reduces how much a CPU can turbo", while you are pointing out "it will not reduce frequency below the regular marked frequency". Say marked freq is 3.4 and the CPU turbos to 3.9. GP is saying an AVX2 instruction will drop it from 3.9 to 3.7 or 3.5, while you're saying it won't drop it below 3.4.