Re: [Qemu-devel] [PATCH 6/8] spapr: init CPUState->cpu_index with index relative to core-id

[David Gibson <david@gibson.dropbear.id.au>]

[-- Attachment #1: Type: text/plain, Size: 1973 bytes --]

On Thu, Jul 21, 2016 at 05:54:37PM +0200, Igor Mammedov wrote:
> It will enshure that cpu_index for a given cpu stays the same
> regardless of the order cpus has been created/deleted and so
> it would be possible to migrate QEMU instance with out of order
> created CPU.
> 
> Signed-off-by: Igor Mammedov <imammedo@redhat.com>

So, this isn't quite right (it wasn't right in my version either).

The problem occurs when smp_threads < kvmppc_smt_threads().  That is,
when the requested threads-per-core is less than the hardware's
maximum number of threads-per-core.

The core-id values are assigned essentially as i *
kvmppc_smt_threads(), meaning the patch below will leave gaps in the
cpu_index values and the last ones will exceed max_cpus, causing other
problems.

What I'm not sure about is whether the right way to fix this is to
change the core-id values, or to calculate the cpu_index from the
existing core-id values.

> ---
>  hw/ppc/spapr_cpu_core.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/hw/ppc/spapr_cpu_core.c b/hw/ppc/spapr_cpu_core.c
> index 4bfc96b..f68e88d 100644
> --- a/hw/ppc/spapr_cpu_core.c
> +++ b/hw/ppc/spapr_cpu_core.c
> @@ -309,9 +309,13 @@ static void spapr_cpu_core_realize(DeviceState *dev, Error **errp)
>      sc->threads = g_malloc0(size * cc->nr_threads);
>      for (i = 0; i < cc->nr_threads; i++) {
>          char id[32];
> +        CPUState *cs;
> +
>          obj = sc->threads + i * size;
>  
>          object_initialize(obj, size, typename);
> +        cs = CPU(obj);
> +        cs->cpu_index = cc->core_id + i;
>          snprintf(id, sizeof(id), "thread[%d]", i);
>          object_property_add_child(OBJECT(sc), id, obj, &local_err);
>          if (local_err) {

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 819 bytes --]