Re: [Qemu-devel] [PATCH v3 09/19] pc: delay setting number of boot CPUs to machine_done time

[Eduardo Habkost]

On Wed, Jul 06, 2016 at 08:20:45AM +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.

Do you plan to fix the remaining code using smp_cpus? e.g.:

1) x86_cpu_realizefn():
    if (cpu->env.features[FEAT_1_EDX] & CPUID_APIC || smp_cpus > 1) {
            x86_cpu_apic_create(cpu, &local_err);
    [...]
  (Maybe we should simply make realizefn fail if we try to create a second CPU
  using -device or device_add without CPUID_APIC)

2) the smp_cpus checks at hw/i386/kvmvapic.c.

> 
> 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 6691825..3206572 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++;
> +        }
> +    }

Any specific reason you chose to check possible_cpus instead of the
arch-independent CPU list from exec.c? I believe other architectures will be
interested in a generic way to count online CPUs instead of using smp_cpus.

> +    /* set the number of CPUs */
> +    rtc_set_memory(pcms->rtc, 0x5f, boot_cpus - 1);
> +
>      if (bus) {
>          int extra_hosts = 0;
>  
> -- 
> 2.7.0
> 

-- 
Eduardo