[CentOS] HT (Hyper Threading) on CentOS 5.5

Fri Mar 9 10:20:44 UTC 2012
Sorin Srbu <sorin.srbu at orgfarm.uu.se>

-----Original Message-----
From: centos-bounces at centos.org [mailto:centos-bounces at centos.org] On Behalf
Of Peter Kjellström
Sent: den 9 mars 2012 11:05
To: centos at centos.org
Subject: Re: [CentOS] HT (Hyper Threading) on CentOS 5.5

> I know there might be some negative performance issues with certain
> applications, but would you notice it in day-to-day use?

Negative performance due to HT comes in several flavours. Some compute 
intensive loads simply perform a bit better with HT off (usually measureable

but not really noticeable, 1-10% is expected here). Another way HT can cause

you performance degradation is due to incorrect scheduling and/or pinning. 
What happens then is that two threads are (incorrectly) put on the same core

instead of using two cores (impact: ~half performance).

On the positive side, if you have many (preferably independent) threads
often get both better throughput and better system response/latency (more 
"processors" available for the kernel to schedule on).


Thanks! I'll have to speak with our calc-chemists about this. Perhaps there
is something to be gained here performance-wise.