Re: [PATCH RESEND 05/18] i386/cpu: Consolidate the use of topo_info in cpu_x86_cpuid()

[Zhao Liu]

On Wed, Feb 15, 2023 at 11:28:25AM +0800, wangyanan (Y) wrote:
> Date: Wed, 15 Feb 2023 11:28:25 +0800
> From: "wangyanan (Y)" <wangyanan55@huawei.com>
> Subject: Re: [PATCH RESEND 05/18] i386/cpu: Consolidate the use of
>  topo_info in cpu_x86_cpuid()
> 
> 在 2023/2/13 17:36, Zhao Liu 写道:
> > From: Zhao Liu <zhao1.liu@intel.com>
> > 
> > In cpu_x86_cpuid(), there are many variables in representing the cpu
> > topology, e.g., topo_info, cs->nr_cores/cs->nr_threads.
> > 
> > Since the names of cs->nr_cores/cs->nr_threads does not accurately
> > represent its meaning, the use of cs->nr_cores/cs->nr_threads is prone
> > to confusion and mistakes.
> > 
> > And the structure X86CPUTopoInfo names its memebers clearly, thus the
> > variable "topo_info" should be preferred.
> > 
> > Suggested-by: Robert Hoo <robert.hu@linux.intel.com>
> > Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
> > ---
> >   target/i386/cpu.c | 30 ++++++++++++++++++------------
> >   1 file changed, 18 insertions(+), 12 deletions(-)
> > 
> > diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> > index 7833505092d8..4cda84eb96f1 100644
> > --- a/target/i386/cpu.c
> > +++ b/target/i386/cpu.c
> > @@ -5215,11 +5215,15 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t 
> > index, uint32_t count,
> >       uint32_t limit;
> >       uint32_t signature[3];
> >       X86CPUTopoInfo topo_info;
> > +    uint32_t cpus_per_pkg;
> >       topo_info.dies_per_pkg = env->nr_dies;
> >       topo_info.cores_per_die = cs->nr_cores / env->nr_dies;
> >       topo_info.threads_per_core = cs->nr_threads;
> > +    cpus_per_pkg = topo_info.dies_per_pkg * topo_info.cores_per_die *
> > +                   topo_info.threads_per_core;
> > +
> >       /* Calculate & apply limits for different index ranges */
> >       if (index >= 0xC0000000) {
> >           limit = env->cpuid_xlevel2;
> > @@ -5255,8 +5259,8 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, 
> > uint32_t count,
> >               *ecx |= CPUID_EXT_OSXSAVE;
> >           }
> >           *edx = env->features[FEAT_1_EDX];
> > -        if (cs->nr_cores * cs->nr_threads > 1) {
> > -            *ebx |= (cs->nr_cores * cs->nr_threads) << 16;
> > +        if (cpus_per_pkg > 1) {
> > +            *ebx |= cpus_per_pkg << 16;
> >               *edx |= CPUID_HT;
> >           }
> >           if (!cpu->enable_pmu) {
> > @@ -5293,10 +5297,12 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t 
> > index, uint32_t count,
> >                */
> >               if (*eax & 31) {
> >                   int host_vcpus_per_cache = 1 + ((*eax & 0x3FFC000) >> 14);
> > -                int vcpus_per_socket = cs->nr_cores * cs->nr_threads;
> > -                if (cs->nr_cores > 1) {
> > +                int vcpus_per_socket = cpus_per_pkg;
> Would it make sense to directly use cpus_per_pkg here
> > +                int cores_per_socket = topo_info.cores_per_die *
> > +                                       topo_info.dies_per_pkg;
> There are other places in cpu_x86_cpuid where cs->nr_cores is used
> separately, why not make a global "cores_per_pkg" like cpus_per_pkg
> and also tweak the other places?

Yeah, good idea.

> > +                if (cores_per_socket > 1) {
> >                       *eax &= ~0xFC000000;
> > -                    *eax |= (pow2ceil(cs->nr_cores) - 1) << 26;
> > +                    *eax |= (pow2ceil(cores_per_socket) - 1) << 26;
> >                   }
> >                   if (host_vcpus_per_cache > vcpus_per_socket) {
> >                       *eax &= ~0x3FFC000;
> > @@ -5436,12 +5442,12 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t 
> > index, uint32_t count,
> >           switch (count) {
> >           case 0:
> >               *eax = apicid_core_offset(&topo_info);
> > -            *ebx = cs->nr_threads;
> > +            *ebx = topo_info.threads_per_core;
> There are many other places in cpu_x86_cpuid where cs->nr_threads
> is used separately, such as encode_cache_cpuid4(***), should we
> replace them all?

In a previous patch [1], I replaced the use of cs->nr_threads/nr_cores in
the call of encode_cache_cpuid4().

The cleanest way is to pass topo_info to encode_cache_cpuid4(), but this
involves the modification of the interface format and the use of the
cache topo level, so I included it in a follow-up patch [2].

[1]: [PATCH RESEND 04/18] i386/cpu: Fix number of addressable IDs in
     CPUID.04,
     https://lists.gnu.org/archive/html/qemu-devel/2023-02/msg03188.html
[2]: [PATCH RESEND 15/18] i386: Use CPUCacheInfo.share_level to encode
     CPUID[4].EAX[bits 25:14],
     https://lists.gnu.org/archive/html/qemu-devel/2023-02/msg03199.html

> >               *ecx |= CPUID_TOPOLOGY_LEVEL_SMT;
> >               break;
> >           case 1:
> >               *eax = apicid_pkg_offset(&topo_info);
> > -            *ebx = cs->nr_cores * cs->nr_threads;
> > +            *ebx = cpus_per_pkg;
> >               *ecx |= CPUID_TOPOLOGY_LEVEL_CORE;
> >               break;
> >           default:
> > @@ -5472,7 +5478,7 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, 
> > uint32_t count,
> >           switch (count) {
> >           case 0:
> >               *eax = apicid_core_offset(&topo_info);
> > -            *ebx = cs->nr_threads;
> > +            *ebx = topo_info.threads_per_core;
> >               *ecx |= CPUID_TOPOLOGY_LEVEL_SMT;
> >               break;
> >           case 1:
> > @@ -5482,7 +5488,7 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, 
> > uint32_t count,
> >               break;
> >           case 2:
> >               *eax = apicid_pkg_offset(&topo_info);
> > -            *ebx = cs->nr_cores * cs->nr_threads;
> > +            *ebx = cpus_per_pkg;
> >               *ecx |= CPUID_TOPOLOGY_LEVEL_DIE;
> >               break;
> >           default:
> > @@ -5707,7 +5713,7 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, 
> > uint32_t count,
> >            * discards multiple thread information if it is set.
> >            * So don't set it here for Intel to make Linux guests happy.
> >            */
> > -        if (cs->nr_cores * cs->nr_threads > 1) {
> > +        if (cpus_per_pkg > 1) {
> >               if (env->cpuid_vendor1 != CPUID_VENDOR_INTEL_1 ||
> >                   env->cpuid_vendor2 != CPUID_VENDOR_INTEL_2 ||
> >                   env->cpuid_vendor3 != CPUID_VENDOR_INTEL_3) {
> > @@ -5769,7 +5775,7 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, 
> > uint32_t count,
> >                *eax |= (cpu_x86_virtual_addr_width(env) << 8);
> >           }
> >           *ebx = env->features[FEAT_8000_0008_EBX];
> > -        if (cs->nr_cores * cs->nr_threads > 1) {
> > +        if (cpus_per_pkg > 1) {
> >               /*
> >                * Bits 15:12 is "The number of bits in the initial
> >                * Core::X86::Apic::ApicId[ApicId] value that indicate
> > @@ -5777,7 +5783,7 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, 
> > uint32_t count,
> >                * Bits 7:0 is "The number of threads in the package is NC+1"
> >                */
> >               *ecx = (apicid_pkg_offset(&topo_info) << 12) |
> > -                   ((cs->nr_cores * cs->nr_threads) - 1);
> > +                   (cpus_per_pkg - 1);
> >           } else {
> >               *ecx = 0;
> >           }
> Thanks,
> Yanan