Re: [PATCH] i386: Add new CPU model SapphireRapids

[Yang Zhong <yang.zhong@linux.intel.com>]

On Mon, Sep 26, 2022 at 09:51:13AM +0100, Dr. David Alan Gilbert wrote:
> * Yang Zhong (yang.zhong@linux.intel.com) wrote:
> > On Sat, Sep 24, 2022 at 12:01:16AM +0800, Xiaoyao Li wrote:
> > > On 9/23/2022 9:30 PM, Yang Zhong wrote:
> > > > On Wed, Sep 21, 2022 at 03:51:42PM +0100, Dr. David Alan Gilbert wrote:
> > > > > * Wang, Lei (lei4.wang@intel.com) wrote:
> > > > > > The new CPU model mostly inherits features from Icelake-Server, while
> > > > > > adding new features:
> > > > > >   - AMX (Advance Matrix eXtensions)
> > > > > >   - Bus Lock Debug Exception
> > > > > > and new instructions:
> > > > > >   - AVX VNNI (Vector Neural Network Instruction):
> > > > > >      - VPDPBUS: Multiply and Add Unsigned and Signed Bytes
> > > > > >      - VPDPBUSDS: Multiply and Add Unsigned and Signed Bytes with Saturation
> > > > > >      - VPDPWSSD: Multiply and Add Signed Word Integers
> > > > > >      - VPDPWSSDS: Multiply and Add Signed Integers with Saturation
> > > > > >   - FP16: Replicates existing AVX512 computational SP (FP32) instructions
> > > > > >     using FP16 instead of FP32 for ~2X performance gain
> > > > > >   - SERIALIZE: Provide software with a simple way to force the processor to
> > > > > >     complete all modifications, faster, allowed in all privilege levels and
> > > > > >     not causing an unconditional VM exit
> > > > > >   - TSX Suspend Load Address Tracking: Allows programmers to choose which
> > > > > >     memory accesses do not need to be tracked in the TSX read set
> > > > > >   - AVX512_BF16: Vector Neural Network Instructions supporting BFLOAT16
> > > > > >     inputs and conversion instructions from IEEE single precision
> > > > > > 
> > > > > > Features may be added in future versions:
> > > > > >   - CET (virtualization support hasn't been merged)
> > > > > > Instructions may be added in future versions:
> > > > > >   - fast zero-length MOVSB (KVM doesn't support yet)
> > > > > >   - fast short STOSB (KVM doesn't support yet)
> > > > > >   - fast short CMPSB, SCASB (KVM doesn't support yet)
> > > > > > 
> > > > > > Signed-off-by: Wang, Lei <lei4.wang@intel.com>
> > > > > > Reviewed-by: Robert Hoo <robert.hu@linux.intel.com>
> > > > > 
> > > > > Hi,
> > > > >     What fills in the AMX tile and tmul information leafs
> > > > > (0x1D, 0x1E)?
> > > > >    In particular, how would we make sure when we migrate between two
> > > > > generations of AMX/Tile/Tmul capable devices with different
> > > > > register/palette/tmul limits that the migration is tied to the CPU type
> > > > > correctly?
> > > > >    Would you expect all devices called a 'SappireRapids' to have the same
> > > > > sizes?
> > > > > 
> > > > 
> > > >     There is only one palette in current design. This palette include 8
> > > >     tiles.  Those two CPUID leafs defined bytes_per_tile, total_tile_bytes,
> > > >     max_rows and etc, the AMX tool will configure those values into TILECFG with
> > > >     ldtilecfg instrcutions. Once tiles are configured, we can use
> > > >     tileload instruction to load data into those tiles.
> > > > 
> > > >     We did migration between two SappireRapids with amx self test tool
> > > >     (tools/testing/selftests/x86/amx.c)started in two sides, the migration
> > > >     work well.
> > > > 
> > > >     As for SappireRapids and more newer cpu types, those two CPUID leafs
> > > >     definitions are all same on AMX.
> > > 
> > > I'm not sure what definitions mean here. Are you saying the CPUID values of
> > > leaf 0x1D and 0x1E won't change for any future Intel Silicion?
> > > 
> > > Personally, I doubt it. And we shouldn't take such assumption unless Intel
> > > states it SDM.
> > 
> >   The current 0x1D and 0x1E definitions as below:
> > 
> >   /* CPUID Leaf 0x1D constants: */
> >   #define INTEL_AMX_TILE_MAX_SUBLEAF     0x1
> >   #define INTEL_AMX_TOTAL_TILE_BYTES     0x2000
> >   #define INTEL_AMX_BYTES_PER_TILE       0x400
> >   #define INTEL_AMX_BYTES_PER_ROW        0x40
> >   #define INTEL_AMX_TILE_MAX_NAMES       0x8
> >   #define INTEL_AMX_TILE_MAX_ROWS        0x10
> > 
> >   /* CPUID Leaf 0x1E constants: */
> >   #define INTEL_AMX_TMUL_MAX_K           0x10
> >   #define INTEL_AMX_TMUL_MAX_N           0x40
> > 
> >   These values are defined from SDM, and from the new developping CPU,
> >   these values are still same with SappireRapids. thanks!
> 
> But there's nothing stopping them increasing in future versions ?
>
  Okay, thanks! We will add these CPUID leafs in this cpu model.

  Yang
  
> Dave
> 
> >   Yang
> > > 
> > > > So, on AMX perspective, the migration
> > > >     should be workable on subsequent cpu types. thanks!
> > > 
> > > I think what Dave worried is that when migrating one VM created with
> > > "SapphireRapids" model on SPR machine to some newer platform in the future,
> > > where the newer platform reports different value on CPUID leaves 0x1D and
> > > 0x1E than SPR platform.
> > > 
> > > I think we need to contain CPUID leaves 0x1D and 0x1E into CPU model as
> > > well. Otherwise we will hit the same as Intel PT that SPR reports less
> > > capabilities that ICX.
> > > 
> > 
> -- 
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
> 
>