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SubjectRe: [PATCH] 2.6.0 batch scheduling, HT aware
On Fri, 2 Jan 2004 Valdis.Kletnieks@vt.edu wrote:

> On Fri, 02 Jan 2004 12:56:16 PST, Davide Libenzi said:
> > On Fri, 2 Jan 2004, Bill Davidsen wrote:
> >
> > > Yes and even worse, if you stop running setiathome the scientific task
> > > *still* only gets half the available CPU!
> >
> > Look that this is not true. If one core is not running any task, the idle
> > task (if not polling) does "hlt" and the "what they call Fetch And
>
> What Bill said was:
>
> >> memory-bound seti&home at CPU1. Even without hyperthreading, your
> >> scientific task is going to run at 50% of speed and seti&home is going
> >> to get second half. Oops.
>
> > Yes and even worse, if you stop running setiathome the scientific task
> > *still* only gets half the available CPU!
>
> So Bill is pointing out that on a *normal* SMP, you get 50% whether or
> not the other processor is busy.

Define 50% ;) In case you are talking about 50% of all the available
resources, in case of a 2 way SMP this is pretty obvious since a
single thread cannot run simultaneuosly on two CPUs. In case of an HT
core, this is not true since the single thread will expand using the whole
core resources. Note though that it won't be an expansion to 100%, and
this is the reason of the existence of the HT technology. That is, even
with monster length pipelines, the CPU is not able to keep exec units 100%
full using a single dispatch unit.



- Davide


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