Hyperthreading degrades performance?
rwatson at FreeBSD.org
Thu Aug 25 16:37:13 GMT 2005
On Thu, 25 Aug 2005, Justin R. Smith wrote:
> This is in reply to the people who said this because of
> cache-contention. Has anyone benchmarked this?
> There's an article
> that benchmarks hyperthreading in Linux and shows a modest (~29%)
> improvement in performance --- depending on applications (with java
> showing degradation of performance). Perhaps the linux sheduler does
> things differently...
In in the last couple of years, I've seen some changes in how we interact
with HTT. 2-3 years ago, when benchmarking MySQL with and without HTT, I
saw a 30%+ drop-off when HTT was enabled. Now, they come out about the
same. I previously also saw no improvement with buildkernel, but recently
I've seen credible reports of build improvements when running with HTT.
So I think that things have changed a bit as a result of significant
scheduler improvements in the last few years, as well as reduced lock
contention. A continued slight decrease in performance for some
benchmarks wouldn't surprise me, but seeing more in the way of "break
even" or even "improvement" strikes me as likely. A thorough revisiting
of the issue would be quite useful :-).
Robert N M Watson
More information about the freebsd-current