Messages in this thread | | | Date | Thu, 03 Dec 2009 10:31:11 +0100 | From | Christian Ehrhardt <> | Subject | Re: Missing recalculation of scheduler tunables in case of cpu hot add/remove |
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Pavel Machek wrote: > Hi! > > >>>>>> Aside from that, we probably should put an upper limit in place, as I >>>>>> guess large cpu count machines get silly large values >>>>>> >>>>>> >>>>> I agree to that, but in the code is already an upper limit of >>>>> 200.000.000 - well we might discuss if that is too low/high. >>>>> >>>>> >>>> Yeah, I think we should cap it around the 8-16 CPUs. >>>> >>>> >>>> >>> ok for me, driven by that finding I think I have to measure different >>> kind of scalings anyway, but as usually that takes some time :-/ >>> At least too time much for the discussion & solution of that bug I guess. >>> >>> The question for now is what we do on cpu hot add/remove? >>> Would hooking somewhere in kernel/cpu.c be the right approach - I'm not >>> quite sure about my own suggestion yet :-). >>> >> Something like the below might work I suppose, just needs a cleanup and >> such. >> > > I see a rather fundamental problem: what if user wants to override > those values, and wants them stay that way Yep a fundamental problem, but fortunately solved already ;-)
See the series "[PATCH 0/3] fix rescaling of scheduler tunables v2" posted after this discussion. That is exactly what patch #2 is about. Giving users the choice to either set things constant (scaling=none) or dynamic (log or linear) as it is done boot time.
As I considered it a bug to miss the updates, the current patch initializes it with scaling=log to let runtime and boot behave the same way. I could do an update to better keep interfaces which would initialize it with "scaling=none" to reflect by default the behavior of the current code that is missing scaling completely. Comments welcome
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Grüsse / regards, Christian Ehrhardt IBM Linux Technology Center, Open Virtualization
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