Re: [PATCH] 2.6.0 batch scheduling, HT aware

[Nick Piggin <piggin@cyberone.com.au>]

Con Kolivas wrote:

>On Tue, 23 Dec 2003 12:36, Nick Piggin wrote:
>
>>Con Kolivas wrote:
>>
>>>I discussed this with Ingo and that's the sort of thing we thought of.
>>>Perhaps a relative crossover of 10 dynamic priorities and an absolute
>>>crossover of 5 static priorities before things got queued together. This
>>>is really only required for the UP HT case.
>>>
>>Well I guess it would still be nice for "SMP HT" as well. Hopefully the
>>code can be generic enough that it would just carry over nicely. 
>>
>
>I disagree. I can't think of a real world scenario where 2+ physical cpus 
>would benefit from this.
>

Well its the same problem. A nice -20 process can still lose 40-55% of its
performance to a nice 19 process, a figure of 10% is probably too high and
we'd really want it <= 5% like what happens with a single logical processor.

>
>>It does 
>>have complications though because the load balancer would have to be taught
>>about it, and those architectures that do hardware priorities probably
>>don't even want it.
>>
>
>Probably the simple relative/absolute will have to suffice. However it still 
>doesn't help the fact that running something cpu bound concurrently at nice 0 
>with something interactive nice 0 is actually slower if you use a UP HT 
>processor in SMP mode instead of UP.
>

It will be based on dynamic priorities, possibly with some feedback from
nice as well, but it probably still won't be perfect and it will probably
be very complex *cough* hardware priorities *cough* ;)

I might try to fit it into a more general priority balancing system because
we currently have similar sorts of failings on regular SMP as well.