On Fri, Sep 22, 2023 at 02:27:18PM -0500, Moger, Babu wrote:
> Date: Fri, 22 Sep 2023 14:27:18 -0500
> From: "Moger, Babu" <bmoger@xxxxxxx>
> Subject: Re: [PATCH v4 19/21] i386: Use offsets get NumSharingCache for
> CPUID[0x8000001D].EAX[bits 25:14]
>
>
> On 9/14/2023 2:21 AM, Zhao Liu wrote:
> > From: Zhao Liu <zhao1.liu@xxxxxxxxx>
> >
> > The commit 8f4202fb1080 ("i386: Populate AMD Processor Cache Information
> > for cpuid 0x8000001D") adds the cache topology for AMD CPU by encoding
> > the number of sharing threads directly.
> >
> > From AMD's APM, NumSharingCache (CPUID[0x8000001D].EAX[bits 25:14])
> > means [1]:
> >
> > The number of logical processors sharing this cache is the value of
> > this field incremented by 1. To determine which logical processors are
> > sharing a cache, determine a Share Id for each processor as follows:
> >
> > ShareId = LocalApicId >> log2(NumSharingCache+1)
> >
> > Logical processors with the same ShareId then share a cache. If
> > NumSharingCache+1 is not a power of two, round it up to the next power
> > of two.
> >
> > From the description above, the calculation of this field should be same
> > as CPUID[4].EAX[bits 25:14] for Intel CPUs. So also use the offsets of
> > APIC ID to calculate this field.
> >
> > [1]: APM, vol.3, appendix.E.4.15 Function 8000_001Dh--Cache Topology
> > Information
> >
> > Signed-off-by: Zhao Liu <zhao1.liu@xxxxxxxxx>
> Reviewed-by: Babu Moger <babu.moger@xxxxxxx>
Thanks Babu!
-Zhao
> > ---
> > Changes since v3:
> > * Rewrite the subject. (Babu)
> > * Delete the original "comment/help" expression, as this behavior is
> > confirmed for AMD CPUs. (Babu)
> > * Rename "num_apic_ids" (v3) to "num_sharing_cache" to match spec
> > definition. (Babu)
> >
> > Changes since v1:
> > * Rename "l3_threads" to "num_apic_ids" in
> > encode_cache_cpuid8000001d(). (Yanan)
> > * Add the description of the original commit and add Cc.
> > ---
> > target/i386/cpu.c | 10 ++++------
> > 1 file changed, 4 insertions(+), 6 deletions(-)
> >
> > diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> > index 5d066107d6ce..bc28c59df089 100644
> > --- a/target/i386/cpu.c
> > +++ b/target/i386/cpu.c
> > @@ -482,7 +482,7 @@ static void encode_cache_cpuid8000001d(CPUCacheInfo *cache,
> > uint32_t *eax, uint32_t *ebx,
> > uint32_t *ecx, uint32_t *edx)
> > {
> > - uint32_t l3_threads;
> > + uint32_t num_sharing_cache;
> > assert(cache->size == cache->line_size * cache->associativity *
> > cache->partitions * cache->sets);
> > @@ -491,13 +491,11 @@ static void encode_cache_cpuid8000001d(CPUCacheInfo *cache,
> > /* L3 is shared among multiple cores */
> > if (cache->level == 3) {
> > - l3_threads = topo_info->modules_per_die *
> > - topo_info->cores_per_module *
> > - topo_info->threads_per_core;
> > - *eax |= (l3_threads - 1) << 14;
> > + num_sharing_cache = 1 << apicid_die_offset(topo_info);
> > } else {
> > - *eax |= ((topo_info->threads_per_core - 1) << 14);
> > + num_sharing_cache = 1 << apicid_core_offset(topo_info);
> > }
> > + *eax |= (num_sharing_cache - 1) << 14;
> > assert(cache->line_size > 0);
> > assert(cache->partitions > 0);
