Re: [Qemu-devel] [PATCH 8/8] [PATCH RFC v2] s390-qemu: cpu hotplug - Treat S390 cpus as devices

[Igor Mammedov <imammedo@redhat.com>]

On Tue, 30 Jul 2013 10:27:26 -0400
"Jason J. Herne" <jjherne@linux.vnet.ibm.com> wrote:

> On 07/30/2013 03:24 AM, Igor Mammedov wrote:
> > On Mon, 29 Jul 2013 15:41:57 -0400
> > "Jason J. Herne" <jjherne@linux.vnet.ibm.com> wrote:
> >
> >> On 06/08/2013 09:11 PM, Andreas Färber wrote:
> >>>>    if (tcg_enabled() && !inited) {
> >>>>>           inited = true;
> >>>>>           s390x_translate_init();
> >>>>>       }
> >>>>> +
> >>>>> +    smp_cpus += 1;
> >>> Won't we need some form of locking?
> >>>
> >>> If we fiddle with a global CPU counter, we should do so in qom/cpu.c,
> >>> not just in s390x code.
> >>>
> >>
> >> I've redesigned a lot of this to make it simpler and less intrusive.
> >> I'm almost ready to post the next revision but I'm hung up on this one
> >> thing.
> >>
> >> I moved the smp_cpu increment to qom/cpu.c : cpu_common_realizefn.
> >> However this seems to break the user mode target because smp_cpus does
> >> not exist.  I tried wrapping the increment in a #ifndef CONFIG_USER_ONLY
> >> statement but it seems to have no effect.  I think the reason for that
> >> is because CONFIG_USER_ONLY is added to config-target.h which is not
> >> actually generated until after we compile qom/cpu.c.
> >>
> >> ...
> >>     CC    qom/object.o
> >>     CC    qom/container.o
> >>     CC    qom/qom-qobject.o
> >>     CC    qom/cpu.o
> >>     CC    hw/core/qdev.o
> >>     CC    hw/core/qdev-properties.o
> >>     CC    hw/core/irq.o
> >>     GEN   s390x-linux-user/config-target.h
> >>     CC    s390x-linux-user/exec.o
> >> ...
> >>
> >> Is there another place I should put the increment?
> >
> > Could you just use current number of cpus instead of smp_cpus increment?
> >
> 
> Is there an easier way of getting the count besides this?
> 
> int cpu_count = 0;
> for (cpu = first_cpu; cpu != NULL; cpu = cpu->next_cpu) {
>      cpu_count++;
> }

maybe qemu_for_each_cpu(), direct access to first_cpu & co is not encouraged.