Messages in this thread | | | Date | Tue, 10 Jan 2006 22:21:29 -0800 | From | "Martin J. Bligh" <> | Subject | Re: -mm seems significanty slower than mainline on kernbench |
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Peter Williams wrote:
> Peter Williams wrote: > >> Con Kolivas wrote: >> >>> On Wed, 11 Jan 2006 01:38 pm, Peter Williams wrote: >>> >>>> Con Kolivas wrote: >>>> > I guess we need to check whether reversing this patch helps. >>>> >>>> It would be interesting to see if it does. >>>> >>>> If it does we probably have to wear the cost (and try to reduce it) as >>>> without this change smp nice support is fairly ineffective due to the >>>> fact that it moves exactly the same tasks as would be moved without >>>> it. >>>> At the most it changes the frequency at which load balancing occurs. >>> >>> >>> >>> >>> I disagree. I think the current implementation changes the balancing >>> according to nice much more effectively than previously where by >>> their very nature, low priority tasks were balanced more frequently >>> and ended up getting their own cpu. >> >> >> >> I can't follow the logic here and I certainly don't see much >> difference in practice. > > > I think I've figured out why I'm not seeing much difference in > practice. I'm only testing on 2 CPU systems and it seems to me that > the main difference that the SMP nice patch will have is in selecting > which CPU to steal tasks from (grabbing the one with the highest > priority tasks) and this is a non issue on a 2 CPU system. :-( > > So I should revise my statement to say that it doesn't make much > difference if there's only 2 CPUs. >
If nothing's niced, why would it be affecting scheduling decisions at all? That seems broken to me ?
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