Hi Zhao,
On 8/1/23 05:35, Zhao Liu wrote:
> From: Zhuocheng Ding <[email protected]>
>
> From CPUState.nr_cores' comment, it represents "number of cores within
> this CPU package".
>
> After 003f230e37d7 ("machine: Tweak the order of topology members in
> struct CpuTopology"), the meaning of smp.cores changed to "the number of
> cores in one die", but this commit missed to change CPUState.nr_cores'
> caculation, so that CPUState.nr_cores became wrong and now it
> misses to consider numbers of clusters and dies.
>
> At present, only i386 is using CPUState.nr_cores.
>
> But as for i386, which supports die level, the uses of CPUState.nr_cores
> are very confusing:
>
> Early uses are based on the meaning of "cores per package" (before die
> is introduced into i386), and later uses are based on "cores per die"
> (after die's introduction).
>
> This difference is due to that commit a94e1428991f ("target/i386: Add
> CPUID.1F generation support for multi-dies PCMachine") misunderstood
> that CPUState.nr_cores means "cores per die" when caculated
> CPUID.1FH.01H:EBX. After that, the changes in i386 all followed this
> wrong understanding.
>
> With the influence of 003f230e37d7 and a94e1428991f, for i386 currently
> the result of CPUState.nr_cores is "cores per die", thus the original
> uses of CPUState.cores based on the meaning of "cores per package" are
> wrong when mutiple dies exist:
> 1. In cpu_x86_cpuid() of target/i386/cpu.c, CPUID.01H:EBX[bits 23:16] is
> incorrect because it expects "cpus per package" but now the
> result is "cpus per die".
> 2. In cpu_x86_cpuid() of target/i386/cpu.c, for all leaves of CPUID.04H:
> EAX[bits 31:26] is incorrect because they expect "cpus per package"
> but now the result is "cpus per die". The error not only impacts the
> EAX caculation in cache_info_passthrough case, but also impacts other
> cases of setting cache topology for Intel CPU according to cpu
> topology (specifically, the incoming parameter "num_cores" expects
> "cores per package" in encode_cache_cpuid4()).
> 3. In cpu_x86_cpuid() of target/i386/cpu.c, CPUID.0BH.01H:EBX[bits
> 15:00] is incorrect because the EBX of 0BH.01H (core level) expects
> "cpus per package", which may be different with 1FH.01H (The reason
> is 1FH can support more levels. For QEMU, 1FH also supports die,
> 1FH.01H:EBX[bits 15:00] expects "cpus per die").
> 4. In cpu_x86_cpuid() of target/i386/cpu.c, when CPUID.80000001H is
> caculated, here "cpus per package" is expected to be checked, but in
> fact, now it checks "cpus per die". Though "cpus per die" also works
> for this code logic, this isn't consistent with AMD's APM.
> 5. In cpu_x86_cpuid() of target/i386/cpu.c, CPUID.80000008H:ECX expects
> "cpus per package" but it obtains "cpus per die".
> 6. In simulate_rdmsr() of target/i386/hvf/x86_emu.c, in
> kvm_rdmsr_core_thread_count() of target/i386/kvm/kvm.c, and in
> helper_rdmsr() of target/i386/tcg/sysemu/misc_helper.c,
> MSR_CORE_THREAD_COUNT expects "cpus per package" and "cores per
> package", but in these functions, it obtains "cpus per die" and
> "cores per die".
>
> On the other hand, these uses are correct now (they are added in/after
> a94e1428991f):
> 1. In cpu_x86_cpuid() of target/i386/cpu.c, topo_info.cores_per_die
> meets the actual meaning of CPUState.nr_cores ("cores per die").
> 2. In cpu_x86_cpuid() of target/i386/cpu.c, vcpus_per_socket (in CPUID.
> 04H's caculation) considers number of dies, so it's correct.
> 3. In cpu_x86_cpuid() of target/i386/cpu.c, CPUID.1FH.01H:EBX[bits
> 15:00] needs "cpus per die" and it gets the correct result, and
> CPUID.1FH.02H:EBX[bits 15:00] gets correct "cpus per package".
>
> When CPUState.nr_cores is correctly changed to "cores per package" again
> , the above errors will be fixed without extra work, but the "currently"
> correct cases will go wrong and need special handling to pass correct
> "cpus/cores per die" they want.
>
> Thus in this patch, we fix CPUState.nr_cores' caculation to fit the
s/Thus in this patch, we fix CPUState.nr_cores' caculation/Fix
CPUState.nr_cores' calculation/
Describe your changes in imperative mood also spell check.
Thanks
Babu
> original meaning "cores per package", as well as changing calculation of
> topo_info.cores_per_die, vcpus_per_socket and CPUID.1FH.
>
> In addition, in the nr_threads' comment, specify it represents the
> number of threads in the "core" to avoid confusion, and also add comment
> for nr_dies in CPUX86State.
>
> Fixes: a94e1428991f ("target/i386: Add CPUID.1F generation support for
> multi-dies PCMachine")
> Fixes: 003f230e37d7 ("machine: Tweak the order of topology members in struct
> CpuTopology")
> Signed-off-by: Zhuocheng Ding <[email protected]>
> Co-developed-by: Zhao Liu <[email protected]>
> Signed-off-by: Zhao Liu <[email protected]>
> ---
> Changes since v2:
> * Use wrapped helper to get cores per socket in qemu_init_vcpu().
> Changes since v1:
> * Add comment for nr_dies in CPUX86State. (Yanan)
> ---
> include/hw/core/cpu.h | 2 +-
> softmmu/cpus.c | 2 +-
> target/i386/cpu.c | 9 ++++-----
> target/i386/cpu.h | 1 +
> 4 files changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/include/hw/core/cpu.h b/include/hw/core/cpu.h
> index fdcbe8735258..57f4d50ace72 100644
> --- a/include/hw/core/cpu.h
> +++ b/include/hw/core/cpu.h
> @@ -277,7 +277,7 @@ struct qemu_work_item;
> * See TranslationBlock::TCG CF_CLUSTER_MASK.
> * @tcg_cflags: Pre-computed cflags for this cpu.
> * @nr_cores: Number of cores within this CPU package.
> - * @nr_threads: Number of threads within this CPU.
> + * @nr_threads: Number of threads within this CPU core.
> * @running: #true if CPU is currently running (lockless).
> * @has_waiter: #true if a CPU is currently waiting for the cpu_exec_end;
> * valid under cpu_list_lock.
> diff --git a/softmmu/cpus.c b/softmmu/cpus.c
> index fed20ffb5dd2..984558d7b245 100644
> --- a/softmmu/cpus.c
> +++ b/softmmu/cpus.c
> @@ -630,7 +630,7 @@ void qemu_init_vcpu(CPUState *cpu)
> {
> MachineState *ms = MACHINE(qdev_get_machine());
>
> - cpu->nr_cores = ms->smp.cores;
> + cpu->nr_cores = machine_topo_get_cores_per_socket(ms);
> cpu->nr_threads = ms->smp.threads;
> cpu->stopped = true;
> cpu->random_seed = qemu_guest_random_seed_thread_part1();
> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> index 97ad229d8ba3..50613cd04612 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -6011,7 +6011,7 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index,
> uint32_t count,
> X86CPUTopoInfo topo_info;
>
> topo_info.dies_per_pkg = env->nr_dies;
> - topo_info.cores_per_die = cs->nr_cores;
> + topo_info.cores_per_die = cs->nr_cores / env->nr_dies;
> topo_info.threads_per_core = cs->nr_threads;
>
> /* Calculate & apply limits for different index ranges */
> @@ -6087,8 +6087,7 @@ 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 = env->nr_dies * cs->nr_cores *
> - cs->nr_threads;
> + int vcpus_per_socket = cs->nr_cores * cs->nr_threads;
> if (cs->nr_cores > 1) {
> *eax &= ~0xFC000000;
> *eax |= (pow2ceil(cs->nr_cores) - 1) << 26;
> @@ -6266,12 +6265,12 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index,
> uint32_t count,
> break;
> case 1:
> *eax = apicid_die_offset(&topo_info);
> - *ebx = cs->nr_cores * cs->nr_threads;
> + *ebx = topo_info.cores_per_die * topo_info.threads_per_core;
> *ecx |= CPUID_TOPOLOGY_LEVEL_CORE;
> break;
> case 2:
> *eax = apicid_pkg_offset(&topo_info);
> - *ebx = env->nr_dies * cs->nr_cores * cs->nr_threads;
> + *ebx = cs->nr_cores * cs->nr_threads;
> *ecx |= CPUID_TOPOLOGY_LEVEL_DIE;
> break;
> default:
> diff --git a/target/i386/cpu.h b/target/i386/cpu.h
> index e0771a10433b..7638128d59cc 100644
> --- a/target/i386/cpu.h
> +++ b/target/i386/cpu.h
> @@ -1878,6 +1878,7 @@ typedef struct CPUArchState {
>
> TPRAccess tpr_access_type;
>
> + /* Number of dies within this CPU package. */
> unsigned nr_dies;
> } CPUX86State;
>
--
Thanks
Babu Moger
