Re: [PATCH v1 1/9] s390x: smp: s390x dedicated smp parsing

[Cornelia Huck]

On Wed, Jul 14 2021, Pierre Morel <pmorel@linux.ibm.com> wrote:

> We need a s390x dedicated SMP parsing to handle s390x specificities.
>
> In this patch we only handle threads, cores and sockets for
> s390x:
> - do not support threads, we always have 1 single thread per core
> - the sockets are filled one after the other with the cores
>
> Both these handlings are different from the standard smp_parse
> functionement and reflect the CPU topology in the simple case
> where all CPU belong to the same book.
>
> Topology levels above sockets, i.e. books, drawers, are not
> considered at this stage and will be introduced in a later patch.
>
> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
> ---
>  hw/s390x/s390-virtio-ccw.c | 42 ++++++++++++++++++++++++++++++++++++++
>  1 file changed, 42 insertions(+)
>
> diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
> index e4b18aef49..899d3a4137 100644
> --- a/hw/s390x/s390-virtio-ccw.c
> +++ b/hw/s390x/s390-virtio-ccw.c
> @@ -582,6 +582,47 @@ static ram_addr_t s390_fixup_ram_size(ram_addr_t sz)
>      return newsz;
>  }
>  
> +/*
> + * In S390CCW machine we do not support threads for now,
> + * only sockets and cores.
> + */
> +static void s390_smp_parse(MachineState *ms, QemuOpts *opts)

It seems you based this on an older version of the code? The current
signature of this function since 1e63fe685804 ("machine: pass QAPI
struct to mc->smp_parse") is

void (*smp_parse)(MachineState *ms, SMPConfiguration *config, Error **errp);

That affects your parsing, and also lets you get rid of the ugly exit(1)
statements.

> +{
> +    unsigned cpus    = qemu_opt_get_number(opts, "cpus", 1);
> +    unsigned sockets = qemu_opt_get_number(opts, "sockets", 1);
> +    unsigned cores   = qemu_opt_get_number(opts, "cores", 1);
> +
> +    if (opts) {
> +        if (cpus == 0 || sockets == 0 || cores == 0) {

This behaviour looks different from what we do for other targets: if you
specify the value as 0, a value is calculated from the other values;
here, you error out. It's probably not a good idea to differ.

> +            error_report("cpu topology: "
> +                         "sockets (%u), cores (%u) or number of CPU(%u) "
> +                         "can not be zero", sockets, cores, cpus);
> +            exit(1);
> +        }
> +    }
> +