Il 12/10/20 05:55, William Brown ha scritto: > We always disable hyper-threading on the compute nodes, at the > recommendation of the company that installed it, who reported that it > ran faster that way. Multi-threading has a cost and is not ideal for > compute workloads. It is better for things like web servers where some > tasks are waiting IO or user input. That said, it likely depends on the > CPU and what is true for Intel might not be true for AMD. Well, we did some tests too. Mostly w/ MPI on the newer nodes (2x14x2). We didn't test disabling HT, just "not using" (scheduling a single process per core). Even FPU-intensive jobs (where there should be maximum contention of the FPU between the two threads) seems to be worthwile to use HT. Say a job can process 100 iterations when using a single thread on a reserved core. If I let it use both threads it can process roughly 180 iterations. So every thread is actually about 10% slower, but overall I can get 1.8 times the throughput when using HT.
That's just my very limited experience, but it seems it could be worthwhile to test. -- Diego Zuccato DIFA - Dip. di Fisica e Astronomia Servizi Informatici Alma Mater Studiorum - Università di Bologna V.le Berti-Pichat 6/2 - 40127 Bologna - Italy tel.: +39 051 20 95786
