Re: [Xen-devel] [PATCH 12/16] xen: sched: fix per-socket runqueue creation in credit2

[George Dunlap <george.dunlap@xxxxxxxxxx>]

On 18/03/16 19:05, Dario Faggioli wrote:
> The credit2 scheduler tries to setup runqueues in such
> a way that there is one of them per each socket. However,
> that does not work. The issue is described in bug #36
> "credit2 only uses one runqueue instead of one runq per
> socket" (http://bugs.xenproject.org/xen/bug/36), and a
> solution has been attempted by an old patch series:
> 
>  http://lists.xen.org/archives/html/xen-devel/2014-08/msg02168.html
> 
> Here, we take advantage of the fact that now initialization
> happens (for all schedulers) during CPU_STARTING, so we
> have all the topology information available when necessary.
> 
> This is true for all the pCPUs _except_ the boot CPU. That
> is not an issue, though. In fact, no runqueue exists yet
> when the boot CPU is initialized, so we can just create
> one and put the boot CPU in there.

The loop is a genius idea, Dario! Well done.

One minor nit...

> Signed-off-by: Dario Faggioli <dario.faggioli@xxxxxxxxxx>
> ---
> Cc: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
> Cc: Justin Weaver <jtweaver@xxxxxxxxxx>
> ---
>  xen/common/sched_credit2.c |   59 
> ++++++++++++++++++++++++++++++++------------
>  1 file changed, 43 insertions(+), 16 deletions(-)
> 
> diff --git a/xen/common/sched_credit2.c b/xen/common/sched_credit2.c
> index 4ff26c9..456b9ea 100644
> --- a/xen/common/sched_credit2.c
> +++ b/xen/common/sched_credit2.c
> @@ -53,7 +53,6 @@
>   *  http://wiki.xen.org/wiki/Credit2_Scheduler_Development
>   * TODO:
>   * + Multiple sockets
> - *  - Detect cpu layout and make runqueue map, one per L2 (make_runq_map())
>   *  - Simple load balancer / runqueue assignment
>   *  - Runqueue load measurement
>   *  - Load-based load balancer
> @@ -1972,6 +1971,48 @@ static void deactivate_runqueue(struct csched2_private 
> *prv, int rqi)
>      cpumask_clear_cpu(rqi, &prv->active_queues);
>  }
>  
> +static unsigned int
> +cpu_to_runqueue(struct csched2_private *prv, unsigned int cpu)
> +{
> +    struct csched2_runqueue_data *rqd;
> +    unsigned int rqi;
> +
> +    for ( rqi = 0; rqi < nr_cpu_ids; rqi++ )
> +    {
> +        unsigned int peer_cpu;
> +
> +        /*
> +         * As soon as we come across an uninitialized runqueue, use it.
> +         * In fact, either:
> +         *  - we are initializing the first cpu, and we assign it to
> +         *    runqueue 0. This is handy, especially if we are dealing
> +         *    with the boot cpu (if credit2 is the default scheduler),
> +         *    as we would not be able to use cpu_to_socket() and similar
> +         *    helpers anyway (they're result of which is not reliable yet);
> +         *  - we have gone through all the active runqueues, and have not
> +         *    found anyone whose cpus' topology matches the one we are
> +         *    dealing with, so ativating a new runqueue is what we want.
> +         */

*activating

With that fixed:

Reviewed-by: George Dunlap <george.dunlap@xxxxxxxxxx>


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