Re: [SLUG] Hyperthreading

["Brett Morgan" <brett.morgan@xxxxxxxxx>]

>From wikipedia (http://en.wikipedia.org/wiki/Hyper-threading):

Intel claims up to a 30% speed improvement compared against an otherwise
identical, non-simultaneous
multithreading<http://en.wikipedia.org/wiki/Simultaneous_multithreading>Pentium
4. The performance improvement seen is very application-dependent,
however, and some programs actually slow down slightly when Hyper Threading
Technology is turned on. This is due to the replay
system<http://en.wikipedia.org/wiki/Replay_system>of the Pentium 4
tying up valuable execution resources, thereby starving the
other thread. (The Pentium 4 Prescott core gained a replay queue, which
reduces execution time needed for the replay system, but this is not enough
to completely overcome the performance hit.) However, any performance
degradation is unique to the Pentium 4 (due to various architectural
nuances), and is not characteristic of simultaneous
multithreading<http://en.wikipedia.org/wiki/Simultaneous_multithreading>in
general.

On Fri, Jul 4, 2008 at 10:08 AM, Rev Simon Rumble <simon@xxxxxxxxxx> wrote:

> I have an Intel Xeon 3 gig CPU and have hyperthreading turned on in the
> BIOS.  I've been trying to work out what the advantages and
> disadvantages of this are.
>
> The CPU appears as two CPUs to the machine, which means that
> non-threaded apps don't appear to use the whole CPU.  Is this a correct
> assumption?  For example, using Devede to convert video, the transcode
> process only uses 50% of CPU in top.  If I run another CPU-intensive
> process, the CPU usage in top goes close to 100%.
>
> So would I be correct in assuming that hyperthreading is useful for
> keeping the system responsive under load, but if running single-threaded
> CPU-intensive processes, it'll run faster without hyperthreading?
>
> This machine can actually take another CPU, but finding a suitable one
> and the matching fan and shroud (Dell) doesn't seem to be easy.
>
> --
> Rev Simon Rumble <simon@xxxxxxxxxx>
> www.rumble.net
>
> The Tourist Engineer
> Just because you're on holiday, doesn't mean you're not a geek.
> http://engineer.openguides.org/
>
> "When I was a kid I used to pray every night for a new bicycle. Then I
>  realised that the Lord doesn't work that way so I stole one and asked
>  Him to forgive me."
> - Emo Philips
> --
> SLUG - Sydney Linux User's Group Mailing List - http://slug.org.au/
> Subscription info and FAQs: http://slug.org.au/faq/mailinglists.html
>



-- 

Brett Morgan http://brett.morgan.googlepages.com/