Re: [PATCH 2/3] xen: Have schedulers revise initial placement

[George Dunlap <george.dunlap@citrix.com>]

On 18/07/16 11:28, Dario Faggioli wrote:
> On Fri, 2016-07-15 at 19:02 +0100, George Dunlap wrote:
>> The generic domain creation logic in
>> xen/common/domctl.c:default_vcpu0_location() attempts to try to do
>> initial placement load-balancing by placing vcpu 0 on the least-busy
>> non-primary hyperthread available.  Unfortunately, the logic can end
>> up picking a pcpu that's not in the online mask.  When this is passed
>> to a scheduler such which assumes that the initial assignment is
>> valid, it causes a null pointer dereference looking up the runqueue.
>>
>> Furthermore, this initial placement doesn't take into account hard or
>> soft affinity, or any scheduler-specific knowledge (such as historic
>> runqueue load, as in credit2).
>>
>> To solve this, when inserting a vcpu, always call the per-scheduler
>> "pick" function to revise the initial placement.  This will
>> automatically take all knowledge the scheduler has into account.
>>
>> Signed-off-by: George Dunlap <george.dunlap@citrix.com>
>> ---
>> CC: Dario Faggioli <dario.faggioli@citrix.com>
>> CC: Anshul Makkar <anshul.makkar@citrix.com>
>> CC: Meng Xu <mengxu@cis.upenn.edu>
>> CC: Jan Beulich <jbeulich@suse.com>
>>
> Reviewed-by: Dario Faggioli <dario.faggioli@citrix.com>

Just to clarify - does this cover the sched_rt.c changes as well?

Thanks,
 -George

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