Re: [Qemu-devel] [PATCH v2 09/18] pc: delay setting number of boot CPUs to machine_done time

[Igor Mammedov]

On Mon, 4 Jul 2016 19:42:07 +0300
"Michael S. Tsirkin" <address@hidden> wrote:

> On Mon, Jul 04, 2016 at 06:15:42PM +0200, Igor Mammedov wrote:
> > On Mon, 4 Jul 2016 17:17:51 +0300
> > "Michael S. Tsirkin" <address@hidden> wrote:
> > 
> > > On Fri, Jun 24, 2016 at 06:05:57PM +0200, Igor Mammedov wrote:
> > > > currently present CPUs counter in CMOS only contains
> > > > smp_cpus (i.e. initial CPUs specified with -smp X) and
> > > > doesn't account for CPUs created with -device.
> > > > If VM is started with additional CPUs added with
> > > >  -device, it will hang in BIOS waiting for condition
> > > >    smp_cpus == counted_cpus
> > > > forever as counted_cpus will include -device CPUs as well
> > > > and be more than smp_cpus.
> > > > 
> > > > make present CPUs counter in CMOS to count all CPUs
> > > > (initial and coldplugged with -device) by delaying
> > > > it to machine done time when it possible to count
> > > > CPUs added with -device.
> > > 
> > > what if device_add from HMP is invoked after machine done
> > > but just before bios init?
> > 
> > pc_cpu_plug():
> >   rtc_set_memory(pcms->rtc, 0x5f, rtc_get_memory(pcms->rtc, 0x5f) +
> > 1);
> > 
> > so BIOS will see and count CPU, the same as with cpu-add HMP
> > command.
> 
> It's all rather fragile.
> Can't we call above line for both hotpluggable and non-hotpluggable
> CPUs?
I've looked at it before and answer was: not unless we rewrite half of
machine as rtc is initialized quite a bit after initial CPUs and it has
a lot of deps. That's why I've kept current split of initial vs
hotplugged cpus wrt rtc_set_memory()

> 
> > > 
> > > > 
> > > > Signed-off-by: Igor Mammedov <address@hidden>
> > > > ---
> > > >  hw/i386/pc.c | 12 +++++++++---
> > > >  1 file changed, 9 insertions(+), 3 deletions(-)
> > > > 
> > > > diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> > > > index b4902f4..06c9de1 100644
> > > > --- a/hw/i386/pc.c
> > > > +++ b/hw/i386/pc.c
> > > > @@ -471,9 +471,6 @@ void pc_cmos_init(PCMachineState *pcms,
> > > >      rtc_set_memory(s, 0x5c, val >> 8);
> > > >      rtc_set_memory(s, 0x5d, val >> 16);
> > > >  
> > > > -    /* set the number of CPU */
> > > > -    rtc_set_memory(s, 0x5f, smp_cpus - 1);
> > > > -
> > > >      object_property_add_link(OBJECT(pcms), "rtc_state",
> > > >                               TYPE_ISA_DEVICE,
> > > >                               (Object **)&pcms->rtc,
> > > > @@ -1157,10 +1154,19 @@ void pc_cpus_init(PCMachineState *pcms)
> > > >  static
> > > >  void pc_machine_done(Notifier *notifier, void *data)
> > > >  {
> > > > +    int i, boot_cpus = 0;
> > > >      PCMachineState *pcms = container_of(notifier,
> > > >                                          PCMachineState,
> > > > machine_done); PCIBus *bus = pcms->bus;
> > > >  
> > > > +    for (i = 0; i < pcms->possible_cpus->len; i++) {
> > > > +        if (pcms->possible_cpus->cpus[i].cpu) {
> > > > +            boot_cpus++;
> > > > +        }
> > > > +    }
> > > > +    /* set the number of CPUs */
> > > > +    rtc_set_memory(pcms->rtc, 0x5f, boot_cpus - 1);
> > > > +
> > > >      if (bus) {
> > > >          int extra_hosts = 0;
> > > >  
> > > > -- 
> > > > 1.8.3.1