Re: [Xen-devel] [PATCH 1/3] xen/sched: populate cpupool0 only after all cpus are up

[George Dunlap <dunlapg@umich.edu>]

On Fri, Aug 2, 2019 at 2:08 PM Juergen Gross <jgross@suse.com> wrote:
>
> With core or socket scheduling we need to know the number of siblings
> per scheduling unit before we can setup the scheduler properly. In
> order to prepare that do cpupool0 population only after all cpus are
> up.
>
> With that in place there is no need to create cpupool0 earlier, so
> do that just before assigning the cpus. Initialize free cpus with all
> online cpus at that time in order to be able to add the cpu notifier
> late, too.
>
> Signed-off-by: Juergen Gross <jgross@suse.com>
> ---
> V1: new patch
> ---
>  xen/common/cpupool.c | 18 ++++++++++++++----
>  1 file changed, 14 insertions(+), 4 deletions(-)
>
> diff --git a/xen/common/cpupool.c b/xen/common/cpupool.c
> index f90e496eda..caea5bd8b3 100644
> --- a/xen/common/cpupool.c
> +++ b/xen/common/cpupool.c
> @@ -762,18 +762,28 @@ static struct notifier_block cpu_nfb = {
>      .notifier_call = cpu_callback
>  };
>
> -static int __init cpupool_presmp_init(void)
> +static int __init cpupool_init(void)
>  {
> +    unsigned int cpu;
>      int err;
> -    void *cpu = (void *)(long)smp_processor_id();
> +
>      cpupool0 = cpupool_create(0, 0, &err);
>      BUG_ON(cpupool0 == NULL);
>      cpupool_put(cpupool0);
> -    cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
>      register_cpu_notifier(&cpu_nfb);
> +
> +    spin_lock(&cpupool_lock);
> +
> +    cpumask_copy(&cpupool_free_cpus, &cpu_online_map);
> +
> +    for_each_cpu ( cpu, &cpupool_free_cpus )
> +        cpupool_assign_cpu_locked(cpupool0, cpu);
> +
> +    spin_unlock(&cpupool_lock);

Just to make sure I understand what's happening here -- cpu_callback()
now won't get called with CPU_ONLINE early in the boot process; but it
will still be called with CPU_ONLINE in other circumstances (e.g.,
hot-plug / suspend / whatever)?

If not, then it's probably best to remove CPU_ONLINE from that switch statement.

Sorry that's an overly-basic question; I don't have a good picture for
the cpu state machine.

 -George

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