Re: HT scheduler: is it really correct? or is it feature of HT?

["Tetsuji \"Maverick\" Rai" <tetsuji.rai@gmail.com>]

After several tests, I found the default value is the best also to me.
 Thanks Con for nice advises and hints on scheduler.   It's fun to
see/modify kernel source files.  But I think kernel isn't my higher
priority.

regards,

On 5/19/05, Con Kolivas <kernel@kolivas.org> wrote:
> On Thu, 19 May 2005 08:46 pm, Tetsuji "Maverick" Rai wrote:
> > I've done a temporary minor hacking, which tells kernel only the half
> > value of nice in all processes.  Actually idle percentage was lowered,
> > but the response of the main application became slower (as a matter of
> > course.)
> >
> > I'm not sure which is better..if possible I want to take advantages of
> > each one :)   Am I expecting too much?
> 
> Yes you are. Hyperthreading (currently depending on workload) only gives you
> on average 15-25% more cpu with multiple threads. You can't get something for
> nothing. Either the nice 0 task runs slower because a low priority task is
> bound to the sibling, or it runs at the same speed and the low priority task
> runs for less. If you want the nice 19 task to use more cpu run it at nice 0
> - because this is effectively what you are trying to do. If you want more cpu
> you need extra true physical cpus, not logical cores.
> 
> Your code does not do what you think it is doing either. If you want to change
> the bias between nice levels across logical cores search the code for where
> the value of sd->per_cpu_gain is set. It is currently set to 25% and you want
> to increase it (although as I said you will derive no real world benefit as
> your nice 0 task will just slow down).
> 
> Cheers,
> Con
> 


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