linux-kernel - Re: Missing recalculation of scheduler tunables in case of cpu hot add/remove

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Message-ID: <4B0EAD7B.90601@linux.vnet.ibm.com>
Date:	Thu, 26 Nov 2009 17:31:55 +0100
From:	Christian Ehrhardt <ehrhardt@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Ingo Molnar <mingo@...e.hu>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Holger.Wolf@...ibm.com, epasch@...ibm.com,
	Martin Schwidefsky <schwidefsky@...ibm.com>
Subject: Re: Missing recalculation of scheduler tunables in case of cpu hot
 add/remove

Peter Zijlstra wrote:
> On Thu, 2009-11-26 at 17:25 +0100, Christian Ehrhardt wrote:
>   
>>> 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 :-).

-- 

Grüsse / regards, Christian Ehrhardt
IBM Linux Technology Center, Open Virtualization 

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