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Re: [Xen-devel] [PATCH v2] xen/sched: rework credit2 run-queue allocation

On Thu, 2020-02-20 at 14:39 +0100, Juergen Gross wrote:
> Currently the memory for each run-queue of the credit2 scheduler is
> allocated at the scheduler's init function: for each cpu in the
> system
> a struct csched2_runqueue_data is being allocated, even if the
> current scheduler only handles one physical cpu or is configured to
> work with a single run-queue. As each struct contains 4 cpumasks this
> sums up to rather large memory sizes pretty fast.
> Rework the memory allocation for run-queues to be done only when
> needed, i.e. when adding a physical cpu to the scheduler requiring a
> new run-queue.
> In fact this fixes a bug in credit2 related to run-queue handling:
> cpu_to_runqueue() will return the first free or matching run-queue,
> which ever is found first. So in case a cpu is removed from credit2
> this could result in e.g. run-queue 0 becoming free, so when another
> cpu is added it will in any case be assigned to that free run-queue,
> even if it would have found another run-queue matching later.
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
Reviewed-by: Dario Faggioli <dfaggioli@xxxxxxxx>

Dario Faggioli, Ph.D
Virtualization Software Engineer
SUSE Labs, SUSE https://www.suse.com/
<<This happens because _I_ choose it to happen!>> (Raistlin Majere)

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