By: Aaron Spink (aaronspink.delete@this.notearthlink.net), August 26, 2015 7:25 am
Room: Moderated Discussions
juanrga (nospam.delete@this.juanrga.com) on August 25, 2015 6:01 pm wrote:
>
> Nvidia talk at ISC2015 was much more interesting. They compared two KNL CPUs against Power+CUDA using Amdahl's
> law. At 98% parallel the KNL was competitive. At 90% parallel work the KNL system was about two times slower than
> the Power+CUDA system: ~2 min vs 4.5 min. At 70% parallel work, the KNL system was more than 3x slower.
>
> Wider vector units and less cores had worked better.
>
So much bogusity... First, that's not what he did. What he did was try to play up the low "node" count on summit. They get this node count by disregarding that their "node" is actual several nodes. Second, he then tried to apply some voodoo computer science by saying higher node count equals lower performance (which funny enough has actually been *disproven* by their partner IBM in actual practice!). If you want to do an actual Amdahl's law evaluation, you have to compare the total parallelism requirements of both systems, which are both incredibly high. If anything, it is likely that the Intel system will be running at a higher frequency, thus requiring less parallelism for a given level of performance, but since no one really outside of a select few in the actual government know the actual *paper* specifications of the systems...
>
> Nvidia talk at ISC2015 was much more interesting. They compared two KNL CPUs against Power+CUDA using Amdahl's
> law. At 98% parallel the KNL was competitive. At 90% parallel work the KNL system was about two times slower than
> the Power+CUDA system: ~2 min vs 4.5 min. At 70% parallel work, the KNL system was more than 3x slower.
>
> Wider vector units and less cores had worked better.
>
So much bogusity... First, that's not what he did. What he did was try to play up the low "node" count on summit. They get this node count by disregarding that their "node" is actual several nodes. Second, he then tried to apply some voodoo computer science by saying higher node count equals lower performance (which funny enough has actually been *disproven* by their partner IBM in actual practice!). If you want to do an actual Amdahl's law evaluation, you have to compare the total parallelism requirements of both systems, which are both incredibly high. If anything, it is likely that the Intel system will be running at a higher frequency, thus requiring less parallelism for a given level of performance, but since no one really outside of a select few in the actual government know the actual *paper* specifications of the systems...
