Hacker News Reader

The old version does AVX and the new version doesn't? Thats crazy! AVX can result in a large speedup [1] in codes that would otherwise not vectorized. For already existing codes it can be 20%.

The best strategy may be to work with ec2 or reject the AVX non-compliant instances.

[1] http://www.behardware.com/medias/photos_news/00/30/IMG003051...

View on HN

Neither version does AVX, the old ones because it's not hardware-supported and the new one because it's disabled in the hypervisor. But some packages apparently don't fully check AVX support: they check that the hardware is AVX-able, but they don't check if it's been disabled.

The older hardware (Intel Xeon X5550) for m2.* instances did not support AVX. The newer hardware supports AVX, but to maintain compatibility with the old hardware, it is disabled (but was still advertised, which is what caused the issue).

AVX is turned on in newer instances like the cc2.8xlarge, which maps to the f2 core on PiCloud.

Reply on news.ycombinator.com