Re: [PATCH] Xen sched: Fix multiple runqueues in credit2

[Juergen Gross <juergen.gross@ts.fujitsu.com>]

On 06.02.2014 14:44, Dario Faggioli wrote:
> On gio, 2014-02-06 at 10:13 +0100, Juergen Gross wrote:
>> On 06.02.2014 09:58, Justin Weaver wrote:
>>> This patch attempts to address the issue of the Xen Credit 2
>>> Scheduler only creating one vCPU run queue on multiple physical
>>> processor systems. It should be creating one run queue per
>>> physical processor.
>>>
>>> CPU 0 does not get a starting callback, so it is hard coded to run
>>> queue 0. At the time this happens, socket information is not
>>> available for CPU 0.
>>>
>>> Socket information is available for each individual CPU when each
>>> gets the STARTING callback (I believe socket information is also
>>> available for CPU 0 by that time). This patch adds the following
>>> algorithm...
>>>
>>> IF cpu is on the same socket as CPU 0, add it to run queue 0
>>
>> You should check whether cpu and CPU0 are in the same cpupool.
>>
>> BTW: CPU0 is allowed to be moved to another cpupool, too.
>>
> Good points. However, the code, as it is now, does not look to care much
> about cpupools while constructing this 'one runqueue per socket' thing,
> does it? I mean, what happens, right now, if, either after or credit2
> builds up the runqueues --say one per socket-- two pCPUs from the same
> socket are in different cpupools? It looks to me that things are
> considered orthogonal while, as you say, tthy may not be... I guess I'll
> try that ASAP and let you know...
>
> My point being that, Justing is trying to fix a bug in credit2, which
> says it constructs one runqueue per socket, while it ends up with only
> one runqueue at all. If there is another bug, or buggy behavior, wrt how
> this interacts with cpupools, although we should fix that too, that's
> pre-existent and needs addressing in a dedicated patch (series), isn't
> it?

Now it will construct one runqueue per cpupool. There is one sched_private
structure per cpupool!

I'm not sure what will happen with the change proposed by Justin in case of
multiple credit2 cpupools...


Juergen

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