Re: [PATCH v7 15/16] i386: Use offsets get NumSharingCache for CPUID[0x8000001D].EAX[bits 25:14]

[Zhao Liu]

Hi Xiaoyao,

On Mon, Jan 15, 2024 at 12:27:43PM +0800, Xiaoyao Li wrote:
> Date: Mon, 15 Jan 2024 12:27:43 +0800
> From: Xiaoyao Li <xiaoyao.li@intel.com>
> Subject: Re: [PATCH v7 15/16] i386: Use offsets get NumSharingCache for
>  CPUID[0x8000001D].EAX[bits 25:14]
> 
> On 1/15/2024 11:48 AM, Zhao Liu wrote:
> > Hi Xiaoyao,
> > 
> > On Sun, Jan 14, 2024 at 10:42:41PM +0800, Xiaoyao Li wrote:
> > > Date: Sun, 14 Jan 2024 22:42:41 +0800
> > > From: Xiaoyao Li <xiaoyao.li@intel.com>
> > > Subject: Re: [PATCH v7 15/16] i386: Use offsets get NumSharingCache for
> > >   CPUID[0x8000001D].EAX[bits 25:14]
> > > 
> > > On 1/8/2024 4:27 PM, Zhao Liu wrote:
> > > > From: Zhao Liu <zhao1.liu@intel.com>
> > > > 
> > > > 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
> > > 
> > > this patch can be dropped because we have next patch.
> > 
> > This patch is mainly used to explicitly emphasize the change in encoding
> > way and compliance with AMD spec... I didn't tested on AMD machine, so
> > the more granular patch would make it easier for the community to review
> > and test.
> 
> then please move this patch ahead, e.g., after patch 2.
>

OK. Thanks!
-Zhao