Messages in this thread |  | | Date | Tue, 11 Jun 2019 15:28:22 -0700 | From | Fenghua Yu <> | Subject | Re: [RFC PATCH] x86/cpufeatures: Enumerate new AVX512 bfloat16 instructions |
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On Tue, Jun 11, 2019 at 09:47:02PM +0200, Borislav Petkov wrote: > On Tue, Jun 11, 2019 at 11:19:20AM -0700, Fenghua Yu wrote: > > So can I re-organize word 11 and 12 as follows? > > > > 1. Change word 11 to host scattered features. > > 2. Move the previos features in word 11 and word 12 to word 11: > > /* > > * Extended auxiliary flags: Linux defined - For features scattered in various > > * CPUID levels and sub-leaves like CPUID level 7 and sub-leaf 1, etc, word 19. > > */ > > #define X86_FEATURE_CQM_LLC (11*32+ 0) /* LLC QoS if 1 */ > > #define X86_FEATURE_CQM_OCCUP_LLC (11*32+ 1) /* LLC occupancy monitoring */ > > #define X86_FEATURE_CQM_MBM_TOTAL (11*32+ 2) /* LLC Total MBM monitoring */ > > #define X86_FEATURE_CQM_MBM_LOCAL (11*32+ 3) /* LLC Local MBM monitoring */ > > Yap. > > > 3. Change word 12 to host CPUID.(EAX=7,ECX=1):EAX: > > /* Intel-defined CPU features, CPUID level 0x7:1 (EAX), word 12 */ > > #define X86_FEATURE_AVX512_BF16 (12*32+ 0) /* BFLOAT16 instructions */ > > This needs to be (12*32+ 5) if word 12 is going to map leaf > CPUID.(EAX=7,ECX=1):EAX. > > At least judging from the arch extensions doc which lists EAX as: > > Bits 04-00: Reserved. > Bit 05: AVX512_BF16. Vector Neural Network Instructions supporting BFLOAT16 inputs and conversion instructions from IEEE single precision. > Bits 31-06: Reserved.
Yes, you are absolutely right. I'll defint it as (12*32+ 5).
> > > 4. Do other necessary changes to match the new word 11 and word 12. > > But split in two patches: first does steps 1+2, second patch adds the > new leaf to word 12.
There are two varialbes defined in cpuinfo_x86: x86_cache_max_rmid and x86_cache_occ_scale. c->x86_cache_max_rmid is read from CPUID.0xf.1:ECX and c->x86_cache_occ_scale is read from CPUID.0xf.1:EBX.
After getting X86_FEATURE_CQM_* from scattered, the two variables need to be read from CPUID again. So the code of reading the two variables need to be moved from before init_scattered_cpuid_features(c) to after the function. This make the get_cpu_cap() code awkward.
And the two variables are ONLY used in resctrl monitoring configuration. There is no need to store them in cpuinfo_x86 on each CPU.
I'm thinking to simplify and clean this part of code:
1. In patch #1: - remove the definitions of x86_cache_max_rmid and x86_cache_occ_scale from cpuinfo_x86 - remove assignment of c->x86_cache_max_rmid and c->x86_cache_occ_scale from get_cpu_cap(c) - get r->mon_scale and r->num_rmid in rdt_get_mon_l3_config(r) directly from CPUID.0xf.1:EBX and CPUID.0xf.1:ECX. 2. In patch #2: do steps 1+2 to recycle word 11. After patch #1, I can totally remove the code to get c->x86_cache_max_rmd and c->x86_cache_occ_scale in get_cpu_cap(c). And patch #2 is cleaner. 3. In patch #3: add new word 12 to host CPUID.7.1:EAX
Do you think the patch #1 is necessary and this is a right patch set?
Thanks.
-Fenghua
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