Quote: Originally Posted by Alejandro85
Never heard of anyone saying that it actually reduces performance.
I'm quoting from several years back, near the start of hyperthreading, and before even dual core systems were plentiful.
The performance hit came from having two threads running in a single core, with just one, shared, on-board memory cache.
When a single application runs on a single processor, the on-board cache is efficient, as applications localise their reference patterns.
When two different applications hyperthread on a single core, the cache required is much greater to avoid too many cache misses; the two processes "steal" cache space from each other, and both run significantly slower than they would have if run alone.
Newer processors have probably eliminated this, if only by having larger onboard cache space.
However, you may have solved a problem I had before I retired. We were running Ubuntu on an IBM server with four discrete Xeon cpu's. However, the Ubunto boot always failed if we told it to run in multiprocessor mode; perhaps it sees only one processor if hyperthreading is off? Unlikely, I'd have thought since the four processors were in separate physical modules, so it's unlikely that the CPU count would fall to one, but who knows? It's worth testing. Thanks!