Re: [PATCH v4] i386/cpu: fixup number of addressable IDs for logical processors in the physical package

[Chuang Xu <xuchuangxclwt@bytedance.com>]

Hi Zhao.

On 10/8/24 上午10:55, Zhao Liu wrote:
> Hi Chuang.
>
> Look fine for me, and only some minor nits:
>
> On Mon, Oct 07, 2024 at 04:13:44PM +0800, Chuang Xu wrote:
>> Date: Mon,  7 Oct 2024 16:13:44 +0800
>> From: Chuang Xu <xuchuangxclwt@bytedance.com>
>> Subject: [PATCH v4] i386/cpu: fixup number of addressable IDs for logical
>>   processors in the physical package
>> X-Mailer: git-send-email 2.24.3 (Apple Git-128)
>>
>> When QEMU is started with:
>> -cpu host,migratable=on,host-cache-info=on,l3-cache=off
>> -smp 180,sockets=2,dies=1,cores=45,threads=2
>>
>> Try to execute "cpuid -1 -l 1 -r" in guest, we'll obtain a value of 90 for
>> CPUID.01H.EBX[23:16], while the expected value is 128. And Try to
>> execute "cpuid -1 -l 4 -r" in guest, we'll obtain a value of 63 for
>> CPUID.04H.EAX[31:26] as expected.
> I polished the sentences a bit:
>
> When executing "cpuid -1 -l 1 -r" in the guest, we obtain a value of 90 for
> CPUID.01H.EBX[23:16], whereas the expected value is 128. Additionally,
> executing "cpuid -1 -l 4 -r" in the guest yields a value of 63 for
> CPUID.04H.EAX[31:26], which matches the expected result.
>
>> As (1+CPUID.04H.EAX[31:26]) round up to the nearest power-of-2 integer,
> s/round/rounds/
>
>> we'd beter round up CPUID.01H.EBX[23:16] to the nearest power-of-2
>> integer too. Otherwise we may encounter unexpected results in guest.
>>
>> For example, when QEMU is started with CLI above and xtopology is disabled,
> What's xtopology?
What I want to express here is Extended Topology Enumeration Leaf.
>> guest kernel 5.15.120 uses CPUID.01H.EBX[23:16]/(1+CPUID.04H.EAX[31:26]) to
>> calculate threads-per-core in detect_ht(). Then guest will get "90/(1+63)=1"
>> as the result, even though theads-per-core should actually be 2.
> s/theads-per-core/threads-per-core/
>   
>> So let us round up CPUID.01H.EBX[23:16] to the nearest power-of-2 integer
>> to solve the unexpected result.
>>
>> In addition, we introduce max_thread_number_in_package() instead of
>> using pow2ceil() to be compatible with smp and hybrid.
>>
>> Signed-off-by: Guixiong Wei <weiguixiong@bytedance.com>
>> Signed-off-by: Yipeng Yin <yinyipeng@bytedance.com>
>> Signed-off-by: Chuang Xu <xuchuangxclwt@bytedance.com>
>> ---
>>   target/i386/cpu.c | 8 +++++++-
>>   1 file changed, 7 insertions(+), 1 deletion(-)
>>
>> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
>> index 85ef7452c0..1b4e3b6931 100644
>> --- a/target/i386/cpu.c
>> +++ b/target/i386/cpu.c
>> @@ -261,6 +261,12 @@ static uint32_t max_thread_ids_for_cache(X86CPUTopoInfo *topo_info,
>>       return num_ids - 1;
>>   }
>>   
>> +static uint32_t max_thread_number_in_package(X86CPUTopoInfo *topo_info)
>> +{
>> +    uint32_t num_threads = 1 << apicid_pkg_offset(topo_info);
>> +    return num_threads;
>> +}
>> +
>>   static uint32_t max_core_ids_in_package(X86CPUTopoInfo *topo_info)
>>   {
>>       uint32_t num_cores = 1 << (apicid_pkg_offset(topo_info) -
>> @@ -6462,7 +6468,7 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
>>           }
>>           *edx = env->features[FEAT_1_EDX];
>>           if (threads_per_pkg > 1) {
>> -            *ebx |= threads_per_pkg << 16;
>> +            *ebx |= max_thread_number_in_package(&topo_info) << 16;
> This helper has only 1 caller and its name doesn't distinguish the
> addressable ID, so it's not necessary. I feel it's better to shift
> the bits directly here:
>
> *ebx |= 1 << apicid_pkg_offset(topo_info) << 16;
>
>>               *edx |= CPUID_HT;
>>           }
>>           if (!cpu->enable_pmu) {
>> -- 
>> 2.20.1
>>
> Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Thanks, Later I'll send patch v5.