Re: [Xen-devel] [PATCH v2 2/3] xen: Have schedulers revise initial placement

[Meng Xu <mengxu@xxxxxxxxxxxxx>]

On Mon, Jul 25, 2016 at 11:28 AM, George Dunlap
<george.dunlap@xxxxxxxxxx> 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.
>
> csched2_cpu_pick ASSERTs that the vcpu's pcpu scheduler lock has been
> taken.  Grab and release the lock to minimize time spend with irqs
> disabled.
>
> Signed-off-by: George Dunlap <george.dunlap@xxxxxxxxxx>
> ---
> v2:
> - Actually grab lock before calling vcpu_schedule_lock() to avoid
>   tripping over a new ASSERT
>
> CC: Dario Faggioli <dario.faggioli@xxxxxxxxxx>
> CC: Anshul Makkar <anshul.makkar@xxxxxxxxxx>
> CC: Meng Xu <mengxu@xxxxxxxxxxxxx>
> CC: Jan Beulich <jbeulich@xxxxxxxx>
> ---
>  xen/common/sched_credit.c  |  3 +++
>  xen/common/sched_credit2.c | 11 ++++++++++-
>  xen/common/sched_rt.c      |  3 +++
>  3 files changed, 16 insertions(+), 1 deletion(-)
>


As to sched_rt.c,

Reviewed-by: Meng Xu <mengxu@xxxxxxxxxxxxx>

-----------
Meng Xu
PhD Student in Computer and Information Science
University of Pennsylvania
http://www.cis.upenn.edu/~mengxu/

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