Re: [Qemu-devel] [Qemu-ppc] [PATCH v5 12/36] spapr: initialize VSMT before initializing the IRQ backend

[Cédric Le Goater]

On 11/28/18 10:35 AM, Greg Kurz wrote:
> On Wed, 28 Nov 2018 13:57:14 +1100
> David Gibson <address@hidden> wrote:
> 
>> On Fri, Nov 16, 2018 at 11:57:05AM +0100, Cédric Le Goater wrote:
>>> We will need to use xics_max_server_number() to create the sPAPRXive
>>> object modeling the interrupt controller of the machine which is
>>> created before the CPUs.
>>>
>>> Signed-off-by: Cédric Le Goater <address@hidden>  
>>
>> My only concern here is that this moves the spapr_set_vsmt_mode()
>> before some of the sanity checks in spapr_init_cpus().  Are we certain
>> there are no edge cases that could cause badness?
>>
> 
> The early checks in spapr_init_cpus() filter out topologies that would
> result in partially filled cores. They're only related to the rest of
> the code that creates the boot CPUs. Before commit 1a5008fc17,
> spapr_set_vsmt_mode() was even being called before spapr_init_cpus().
> The rationale to move it there was to ensure it is called before the
> first user of spapr->vsmt, which happens to be a call to
> xics_max_server_number().
> 
> Now that xics_max_server_number() needs to be called even earlier, I think a
> better change is to have xics_max_server_number() to call 
> spapr_set_vsmt_mode()
> if spapr->vsmt isn't set.

That 'smt' routine is black magic to me and I would not dare touching it.

C.
 
> 
>>> ---
>>>  hw/ppc/spapr.c | 10 +++++-----
>>>  1 file changed, 5 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
>>> index 7afd1a175bf2..50cb9f9f4a02 100644
>>> --- a/hw/ppc/spapr.c
>>> +++ b/hw/ppc/spapr.c
>>> @@ -2466,11 +2466,6 @@ static void spapr_init_cpus(sPAPRMachineState *spapr)
>>>          boot_cores_nr = possible_cpus->len;
>>>      }
>>>  
>>> -    /* VSMT must be set in order to be able to compute VCPU ids, ie to
>>> -     * call xics_max_server_number() or spapr_vcpu_id().
>>> -     */
>>> -    spapr_set_vsmt_mode(spapr, &error_fatal);
>>> -
>>>      if (smc->pre_2_10_has_unused_icps) {
>>>          int i;
>>>  
>>> @@ -2593,6 +2588,11 @@ static void spapr_machine_init(MachineState *machine)
>>>      /* Setup a load limit for the ramdisk leaving room for SLOF and FDT */
>>>      load_limit = MIN(spapr->rma_size, RTAS_MAX_ADDR) - FW_OVERHEAD;
>>>  
>>> +    /* VSMT must be set in order to be able to compute VCPU ids, ie to
>>> +     * call xics_max_server_number() or spapr_vcpu_id().
>>> +     */
>>> +    spapr_set_vsmt_mode(spapr, &error_fatal);
>>> +
>>>      /* Set up Interrupt Controller before we create the VCPUs */
>>>      smc->irq->init(spapr, &error_fatal);
>>>    
>>
>