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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <4B0EAC06.3010407@linux.vnet.ibm.com>
Date:	Thu, 26 Nov 2009 17:25:42 +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 17:10 +0100, Christian Ehrhardt wrote:
>
>   
>> What I consider more important at the moment is that there is no hook to 
>> recalculate these values in case cpu hot add/remove takes place.
>> As an example someone could boot a machine with one online cpu and get 
>> the low non scaled defaults, later on driven by load the system 
>> activates more and more processors. Therefore the system could end up 
>> having  a large amount of cpus with non recalculated scheduler tunables.
>>     
>
> This is virt junk that's playing dumb games with hotplug isn't it?
>   
Some sort of, its on s390 which does that all the time. By default there 
is a daemon that activates/deactivates cpus according to load to cover 
load peaks but also save virtualization overhead.
> Normal machines simply don't change their numbers of cpus, if they
> hotplug its usually for things like suspend or actual replacement of a
> faulty piece of kit, in which case there's little point in adjusting
> things.
>
>   
What is still "normal" today, you cant get s390 without virt so I would 
consider it normal and a real use case for us :-)
> 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.


-- 

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

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/