Re: [Qemu-devel] [PATCH v3 10/19] pc: register created initial and hotpluged CPUs in one place pc_cpu_plug()

[Igor Mammedov]

On Thu, 14 Jul 2016 12:03:19 -0300
Eduardo Habkost <address@hidden> wrote:

> On Thu, Jul 14, 2016 at 11:18:36AM +0200, Igor Mammedov wrote:
> > On Wed, 13 Jul 2016 20:37:13 -0300
> > Eduardo Habkost <address@hidden> wrote:
> >   
> > > On Wed, Jul 13, 2016 at 06:59:21PM -0400, Bandan Das wrote:  
> > > > Eduardo Habkost <address@hidden> writes:
> > > >     
> > > > > On Wed, Jul 13, 2016 at 06:32:27PM -0400, Bandan Das wrote:    
> > > > >> Igor Mammedov <address@hidden> writes:
> > > > >>     
> > > > >> > consolidate possible_cpus array management in pc_cpu_plug()
> > > > >> > for smp_cpus, coldplugged with -device and hotplugged with
> > > > >> > device_add.    
> > > > >> 
> > > > >> So, this takes care of the hotplug case and 09/19 took care of the
> > > > >> coldplug case, right ? If yes, we should probably modify this commit
> > > > >> message a little.    
> > > > >
> > > > > This makes pc_cpu_plug() take care of both: now it will handle
> > > > > the coldplug case also (in addition to the hotplug case, that it
> > > > > already handled). I don't understand what you mean.
> > > > >
> > > > > Are you talking about the rtc_set_memory() call, only? This seems
> > > > > to be the only hotplug-specific code that still remains, in this    
> > > > 
> > > > Right, I thought the rtc_set_memory() call in 09/19 takes care of the
> > > > case when the user boots with "-device" and this takes care of the case
> > > > when user invokes device_add, no ?    
> > > 
> > > Yes for rtc_set_memory(). But the main purpose of this patch is
> > > to reuse all the rest of pc_cpu_plug() (i.e. everything except
> > > for the rtc_set_memory() call) for the coldplug CPUs too.
> > > 
> > > Note that I didn't review the patch completely, yet. The
> > > replacement for the possible_cpus code looks OK, but I didn't
> > > check if it is safe to call
> > > HOTPLUG_HANDLER_GET_CLASS(pcms->acpi_dev)->plug() for coldplugged
> > > CPUs too.  
> > for cpus created at  pc_cpus_init() time, that path is unreachable
> > since pcms->acpi_dev == NULL,  
> 
> Sounds fragile, as it requires specific initialization ordering
> in the pc_cpus_init() caller. But:
> 
> > 
> > even if in the future that path becomes reachable
> > (when we could specify all CPUs including BSP with -device, it doesn't work 
> > for BSP yet)
> >  i.e. pcms->acpi_dev != NULL
> > then acpi_device will have be initialized see cpu_hotplug_hw_init()
> > and following plug handler will be called acpi_cpu_plug_cb() doing what
> > it was supposed to do.  
> 
> For reference for others, acpi_cpu_plug_cb() is:
> 
> void acpi_cpu_plug_cb(HotplugHandler *hotplug_dev,
>                       CPUHotplugState *cpu_st, DeviceState *dev, Error **errp)
> {
>     AcpiCpuStatus *cdev;
> 
>     cdev = get_cpu_status(cpu_st, dev);
>     if (!cdev) {
>         return;
>     }
> 
>     cdev->cpu = CPU(dev);
>     if (dev->hotplugged) {
>         cdev->is_inserting = true;
>         acpi_send_event(DEVICE(hotplug_dev), ACPI_CPU_HOTPLUG_STATUS);
>     }
> }
> 
> get_cpu_status() should return non-NULL for all possible CPUs. So the only 
> code
> for coldplug case is cdev->cpu = CPU(dev), which is really something we want 
> to
> run.
> 
> So, that means it works properly on both cases: if pcms->acpi_dev==NULL and if
> pcms->acpi_dev != NULL.
> 
> Reviewed-by: Eduardo Habkost <address@hidden>
> 
> Related question: why does CPUHotplugState needs to duplicate the list of
> (CPUState *cpu, uint64_t arch_id) pairs, if PCMachineState already maintains a
> list with exactly the same information?
It maintains an array of AcpiCpuStatus, which is not only what
PCMachineState::possible_cpus is but an additional ACPI related
hot-plug state for each possible CPU.

Probably PCMachineState::possible_cpus could be used in hw/acpi/cpu.c
but I've not looked at it. It doesn't look like directly accessing
PCMachineState::possible_cpus would give anything beside leaving out
managing AcpiCpuStatus.cpu (which serves as present/missing flag beside
of providing direct access to CPU instance when needed).

And I obviously don't want to push ACPI runtime state into generic
possible_cpus.



> 
> >   
> > >   
> > > >     
> > > > > patch.
> > > > >    
> > > > >> 
> > > > >> Bandan    
> > > > >> > Signed-off-by: Igor Mammedov <address@hidden>
> > > > >> > ---
> > > > >> >  hw/i386/pc.c | 25 +++++++++----------------
> > > > >> >  1 file changed, 9 insertions(+), 16 deletions(-)
> > > > >> >
> > > > >> > diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> > > > >> > index 3206572..0f85b56 100644
> > > > >> > --- a/hw/i386/pc.c
> > > > >> > +++ b/hw/i386/pc.c
> > > > >> > @@ -1142,7 +1142,6 @@ void pc_cpus_init(PCMachineState *pcms)
> > > > >> >          if (i < smp_cpus) {
> > > > >> >              cpu = pc_new_cpu(typename, 
> > > > >> > x86_cpu_apic_id_from_index(i),
> > > > >> >                               &error_fatal);
> > > > >> > -            pcms->possible_cpus->cpus[i].cpu = CPU(cpu);
> > > > >> >              object_unref(OBJECT(cpu));
> > > > >> >          }
> > > > >> >      }
> > > > >> > @@ -1697,25 +1696,19 @@ static void pc_cpu_plug(HotplugHandler 
> > > > >> > *hotplug_dev,
> > > > >> >      Error *local_err = NULL;
> > > > >> >      PCMachineState *pcms = PC_MACHINE(hotplug_dev);
> > > > >> >  
> > > > >> > -    if (!dev->hotplugged) {
> > > > >> > -        goto out;
> > > > >> > -    }
> > > > >> > -
> > > > >> > -    if (!pcms->acpi_dev) {
> > > > >> > -        error_setg(&local_err,
> > > > >> > -                   "cpu hotplug is not enabled: missing acpi 
> > > > >> > device");
> > > > >> > -        goto out;
> > > > >> > +    if (pcms->acpi_dev) {
> > > > >> > +        hhc = HOTPLUG_HANDLER_GET_CLASS(pcms->acpi_dev);
> > > > >> > +        hhc->plug(HOTPLUG_HANDLER(pcms->acpi_dev), dev, 
> > > > >> > &local_err);
> > > > >> > +        if (local_err) {
> > > > >> > +            goto out;
> > > > >> > +        }
> > > > >> >      }
> > > > >> >  
> > > > >> > -    hhc = HOTPLUG_HANDLER_GET_CLASS(pcms->acpi_dev);
> > > > >> > -    hhc->plug(HOTPLUG_HANDLER(pcms->acpi_dev), dev, &local_err);
> > > > >> > -    if (local_err) {
> > > > >> > -        goto out;
> > > > >> > +    if (dev->hotplugged) {
> > > > >> > +        /* increment the number of CPUs */
> > > > >> > +        rtc_set_memory(pcms->rtc, 0x5f, rtc_get_memory(pcms->rtc, 
> > > > >> > 0x5f) + 1);
> > > > >> >      }
> > > > >> >  
> > > > >> > -    /* increment the number of CPUs */
> > > > >> > -    rtc_set_memory(pcms->rtc, 0x5f, rtc_get_memory(pcms->rtc, 
> > > > >> > 0x5f) + 1);
> > > > >> > -
> > > > >> >      found_cpu = pc_find_cpu_slot(pcms, CPU(dev), NULL);
> > > > >> >      found_cpu->cpu = CPU(dev);
> > > > >> >  out:    
> > >   
> >   
>