Re: [RFC PATCH 3/4] i386: Track cores_per_module in CPUX86State

[Xiaoyao Li <xiaoyao.li@intel.com>]

On 12/11/2024 12:43 AM, Igor Mammedov wrote:
> On Thu,  5 Dec 2024 09:57:15 -0500
> Xiaoyao Li <xiaoyao.li@intel.com> wrote:
> 
>> x86 is the only user of CPUState::nr_cores.
>>
>> Define cores_per_module in CPUX86State, which can serve as the
>> substitute of CPUState::nr_cores. After x86 switches to use
>> CPUX86State::cores_per_module, CPUState::nr_cores will lose the only
>> user and QEMU can drop it.
>>
>> Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
>> ---
>>   hw/i386/x86-common.c | 2 ++
>>   target/i386/cpu.c    | 2 +-
>>   target/i386/cpu.h    | 9 +++++++--
>>   3 files changed, 10 insertions(+), 3 deletions(-)
>>
>> diff --git a/hw/i386/x86-common.c b/hw/i386/x86-common.c
>> index dc031af66217..f7a20c1da30c 100644
>> --- a/hw/i386/x86-common.c
>> +++ b/hw/i386/x86-common.c
>> @@ -271,6 +271,8 @@ void x86_cpu_pre_plug(HotplugHandler *hotplug_dev,
>>   
>>       init_topo_info(&topo_info, x86ms);
>>   
>> +    env->nr_cores = ms->smp.cores;
> this doesn't look like the same as in qemu_init_vcpu(),
> which uses machine_topo_get_cores_per_socket()
> Can you clarify the change?

because env->nr_cores has a different meaning vs. cs->nr_cores.

As the below comments of nr_cores in the diff

+    /* Number of cores within one module. */
+    unsigned nr_cores;

it means the number of cores within one module. It uses the similar 
convention as nr_dies and nr_modules in struct CPUArchState.

However, CPUState::nr_cores means the number of cores in the package.

yes, we can keep the same meaning of nr_cores as "number of cores in the 
package" when define it struct CPUArchState. However, it leads to 
inconsistency with nr_dies and nr_modules already there and confuses people.

>> +
>>       if (ms->smp.modules > 1) {
>>           env->nr_modules = ms->smp.modules;
>>           set_bit(CPU_TOPOLOGY_LEVEL_MODULE, env->avail_cpu_topo);
>> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
>> index 3725dbbc4b3f..15b50c44ae79 100644
>> --- a/target/i386/cpu.c
>> +++ b/target/i386/cpu.c
>> @@ -6503,7 +6503,7 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
>>   
>>       topo_info.dies_per_pkg = env->nr_dies;
>>       topo_info.modules_per_die = env->nr_modules;
>> -    topo_info.cores_per_module = cs->nr_cores / env->nr_dies / env->nr_modules;
>> +    topo_info.cores_per_module = env->nr_cores;
>>       topo_info.threads_per_core = cs->nr_threads;
>>   
>>       cores_per_pkg = topo_info.cores_per_module * topo_info.modules_per_die *
>> diff --git a/target/i386/cpu.h b/target/i386/cpu.h
>> index 5795a497e567..c37a49a1a02b 100644
>> --- a/target/i386/cpu.h
>> +++ b/target/i386/cpu.h
>> @@ -2051,6 +2051,9 @@ typedef struct CPUArchState {
>>       /* Number of modules within one die. */
>>       unsigned nr_modules;
>>   
>> +    /* Number of cores within one module. */
>> +    unsigned nr_cores;
>> +
>>       /* Bitmap of available CPU topology levels for this CPU. */
>>       DECLARE_BITMAP(avail_cpu_topo, CPU_TOPOLOGY_LEVEL__MAX);
>>   } CPUX86State;
>> @@ -2393,10 +2396,12 @@ static inline void cpu_x86_load_seg_cache_sipi(X86CPU *cpu,
>>   static inline uint64_t cpu_x86_get_msr_core_thread_count(X86CPU *cpu)
>>   {
>>       CPUState *cs = CPU(cpu);
>> +    CPUX86State *env = &cpu->env;
>>       uint64_t val;
>> +    uint64_t cores_per_package = env->nr_cores * env->nr_modules * env->nr_dies;
>>   
>> -    val = cs->nr_threads * cs->nr_cores;  /* thread count, bits 15..0 */
>> -    val |= ((uint32_t)cs->nr_cores << 16); /* core count, bits 31..16 */
>> +    val = cs->nr_threads * cores_per_package;  /* thread count, bits 15..0 */
>> +    val |= (cores_per_package << 16); /* core count, bits 31..16 */
>>   
>>       return val;
>>   }
>