>>>>> "Simon" == Simon Rumble <Rev> writes: Simon> I have an Intel Xeon 3 gig CPU and have hyperthreading turned Simon> on in the BIOS. I've been trying to work out what the Simon> advantages and disadvantages of this are.
Simon> The CPU appears as two CPUs to the machine, which means that Simon> non-threaded apps don't appear to use the whole CPU. Is this a Simon> correct assumption? For example, using Devede to convert Simon> video, the transcode process only uses 50% of CPU in top. If I Simon> run another CPU-intensive process, the CPU usage in top goes Simon> close to 100%. This is an incorrect assumption. Linux treats each thread for the purposes of calculating CPU usage as a separate core. So even if one (hyper)thread is using 100% of the processor, it'll show up as 50% usage. If you have more than one running thread/process, hyperthreading typically gives between 1 and 30% increase in throughput (compared with the same processor with SMT turned off). If you have a single thread, then there should be no performance penalty (except that you can probably gain performance by configuring ou kernel a a uniprocessor kernel, and avoiding all the locking overhead). -- Dr Peter Chubb http://www.gelato.unsw.edu.au peterc AT gelato.unsw.edu.au http://www.ertos.nicta.com.au ERTOS within National ICT Australia -- SLUG - Sydney Linux User's Group Mailing List - http://slug.org.au/ Subscription info and FAQs: http://slug.org.au/faq/mailinglists.html
