Re: [PATCH v4 12/16] hw/i386: Use the apicid handlers from X86MachineState

[Babu Moger]

On 2/24/20 11:19 AM, Igor Mammedov wrote:
> On Thu, 13 Feb 2020 12:17:46 -0600
> Babu Moger <address@hidden> wrote:
> 
>> Check and Load the apicid handlers from X86CPUDefinition if available.
>> Update the calling convention for the apicid handlers.
> 
> Previous and this patch look too complicated for the task at the hand.
> In particular, cpu_x86_init_apicid_fns() from previous patch adds 1 more
> reference to Machine into i386/cpu.c (even though it's just a helper function)
> and I think un-necessary hooks to X86CPUDefinition (it's not really CPU's
> businesses to make up APIC-IDs).
> 
> I'd rather do opposite and get rid of the last explicit dependency to
> ms->smp.cpus from cpu.c. But well, it's out of scope of this series,
> so for this series I'd just try to avoid adding more Machine dependencies.
> 
> All 11/16 does is basically using hooks as a switch "I'm EPYC" to
> set epyc specific encoding topo routines.
> 
> It could be accomplished by a simple Boolean flag like
>  X86CPUDefinition::use_epyc_apic_id_encoding
> 
> and then cpu_x86_init_apicid_fns() could be replaced with trivial
> helper like:
> 
>   x86_use_epyc_apic_id_encoding(char *cpu_type)
>   {
>       X86CPUClass *xcc = ... cpu_type ...
>       return xcc->model->cpudef->use_epyc_apic_id_encoding
>   }
> 
> then machine could override default[1] hooks using this helper
> as the trigger
>   x86_cpus_init()
>   {
>       // no need in dedicated function as it's the only instance it's going 
> to be called ever
>       if (x86_use_epyc_apic_id_encoding(ms->cpu_type)) {
>             x86ms->apicid_from_cpu_idx = ...epyc...
>             x86ms->topo_ids_from_apicid = ...epyc...
>             x86ms->apicid_from_topo_ids = ...epyc...
>             x86ms->apicid_pkg_offset = ...epyc...
>       }
>   }
> 
> That would be less invasive and won't create non necessary dependencies.

Yes. We can achieve the task here with your approach mentioned above. But,
we still will have a scaling issue. In future if a "new cpu model" comes
up its own decoding, then we need to add another bolean flag use_new
_cpu_apic_id_encoding. And then do that same check again. In that sense,
the current approach is bit generic. Lets also hear from Eduardo.

> 
> ---
> 1) defaults should be set in x86_machine_class_init()
> 
> Eduardo, what's your take on this?
> 
>> Signed-off-by: Babu Moger <address@hidden>
>> ---
>>  hw/i386/pc.c  |    6 +++---
>>  hw/i386/x86.c |   27 +++++++++++++++++++++++----
>>  2 files changed, 26 insertions(+), 7 deletions(-)
>>
>> diff --git a/hw/i386/pc.c b/hw/i386/pc.c
>> index be72a49716..93063af6a8 100644
>> --- a/hw/i386/pc.c
>> +++ b/hw/i386/pc.c
>> @@ -1808,14 +1808,14 @@ static void pc_cpu_pre_plug(HotplugHandler 
>> *hotplug_dev,
>>          topo_ids.die_id = cpu->die_id;
>>          topo_ids.core_id = cpu->core_id;
>>          topo_ids.smt_id = cpu->thread_id;
>> -        cpu->apic_id = x86_apicid_from_topo_ids(&topo_info, &topo_ids);
>> +        cpu->apic_id = x86ms->apicid_from_topo_ids(&topo_info, &topo_ids);
>>      }
>>  
>>      cpu_slot = pc_find_cpu_slot(MACHINE(pcms), cpu->apic_id, &idx);
>>      if (!cpu_slot) {
>>          MachineState *ms = MACHINE(pcms);
>>  
>> -        x86_topo_ids_from_apicid(cpu->apic_id, &topo_info, &topo_ids);
>> +        x86ms->topo_ids_from_apicid(cpu->apic_id, &topo_info, &topo_ids);
>>          error_setg(errp,
>>              "Invalid CPU [socket: %u, die: %u, core: %u, thread: %u] with"
>>              " APIC ID %" PRIu32 ", valid index range 0:%d",
>> @@ -1836,7 +1836,7 @@ static void pc_cpu_pre_plug(HotplugHandler 
>> *hotplug_dev,
>>      /* TODO: move socket_id/core_id/thread_id checks into 
>> x86_cpu_realizefn()
>>       * once -smp refactoring is complete and there will be CPU private
>>       * CPUState::nr_cores and CPUState::nr_threads fields instead of 
>> globals */
>> -    x86_topo_ids_from_apicid(cpu->apic_id, &topo_info, &topo_ids);
>> +    x86ms->topo_ids_from_apicid(cpu->apic_id, &topo_info, &topo_ids);
>>      if (cpu->socket_id != -1 && cpu->socket_id != topo_ids.pkg_id) {
>>          error_setg(errp, "property socket-id: %u doesn't match set apic-id:"
>>              " 0x%x (socket-id: %u)", cpu->socket_id, cpu->apic_id, 
>> topo_ids.pkg_id);
>> diff --git a/hw/i386/x86.c b/hw/i386/x86.c
>> index 3d944f68e6..b825861b85 100644
>> --- a/hw/i386/x86.c
>> +++ b/hw/i386/x86.c
>> @@ -52,6 +52,22 @@
>>  /* Physical Address of PVH entry point read from kernel ELF NOTE */
>>  static size_t pvh_start_addr;
>>  
>> +/*
>> + * Check for apicid handlers in X86MachineState. Load them if
>> + * not loaded already. These handlers are loaded from X86CPUDefinition.
>> + */
>> +static void x86_check_apicid_handlers(MachineState *ms)
>> +{
>> +    X86MachineState *x86ms = X86_MACHINE(ms);
>> +
>> +    if (!x86ms->apicid_from_cpu_idx ||
>> +        !x86ms->topo_ids_from_apicid ||
>> +        !x86ms->apicid_from_topo_ids ||
>> +        !x86ms->apicid_pkg_offset) {
>> +        cpu_x86_init_apicid_fns(ms);
>> +    }
>> +}
>> +
>>  /*
>>   * Calculates initial APIC ID for a specific CPU index
>>   *
>> @@ -70,7 +86,7 @@ uint32_t x86_cpu_apic_id_from_index(X86MachineState *x86ms,
>>  
>>      init_topo_info(&topo_info, x86ms);
>>  
>> -    correct_id = x86_apicid_from_cpu_idx(&topo_info, cpu_index);
>> +    correct_id = x86ms->apicid_from_cpu_idx(&topo_info, cpu_index);
>>      if (x86mc->compat_apic_id_mode) {
>>          if (cpu_index != correct_id && !warned && !qtest_enabled()) {
>>              error_report("APIC IDs set in compatibility mode, "
>> @@ -148,8 +164,8 @@ int64_t x86_get_default_cpu_node_id(const MachineState 
>> *ms, int idx)
>>     init_topo_info(&topo_info, x86ms);
>>  
>>     assert(idx < ms->possible_cpus->len);
>> -   x86_topo_ids_from_apicid(ms->possible_cpus->cpus[idx].arch_id,
>> -                            &topo_info, &topo_ids);
>> +   x86ms->topo_ids_from_apicid(ms->possible_cpus->cpus[idx].arch_id,
>> +                               &topo_info, &topo_ids);
>>     return topo_ids.pkg_id % ms->numa_state->num_nodes;
>>  }
>>  
>> @@ -169,6 +185,9 @@ const CPUArchIdList 
>> *x86_possible_cpu_arch_ids(MachineState *ms)
>>          return ms->possible_cpus;
>>      }
>>  
>> +    /* Initialize apicid handlers */
>> +    x86_check_apicid_handlers(ms);
>> +
>>      ms->possible_cpus = g_malloc0(sizeof(CPUArchIdList) +
>>                                    sizeof(CPUArchId) * max_cpus);
>>      ms->possible_cpus->len = max_cpus;
>> @@ -182,7 +201,7 @@ const CPUArchIdList 
>> *x86_possible_cpu_arch_ids(MachineState *ms)
>>          ms->possible_cpus->cpus[i].vcpus_count = 1;
>>          ms->possible_cpus->cpus[i].arch_id =
>>              x86_cpu_apic_id_from_index(x86ms, i);
>> -        x86_topo_ids_from_apicid(ms->possible_cpus->cpus[i].arch_id,
>> +        x86ms->topo_ids_from_apicid(ms->possible_cpus->cpus[i].arch_id,
>>                                   &topo_info, &topo_ids);
>>          ms->possible_cpus->cpus[i].props.has_socket_id = true;
>>          ms->possible_cpus->cpus[i].props.socket_id = topo_ids.pkg_id;
>>
>>
>