Re: [PATCH 2/2] iommu/amd: Remove performance counter pre-initialization test

[Shuah Khan]

On 4/9/21 2:00 PM, Shuah Khan wrote:
> On 4/9/21 2:58 AM, Suravee Suthikulpanit wrote:
> > In early AMD desktop/mobile platforms (during 2013), when the IOMMU
> > Performance Counter (PMC) support was first introduced in
> > commit 30861ddc9cca ("perf/x86/amd: Add IOMMU Performance Counter
> > resource management"), there was a HW bug where the counters could not
> > be accessed. The result was reading of the counter always return zero.
> >
> > At the time, the suggested workaround was to add a test logic prior
> > to initializing the PMC feature to check if the counters can be 
> > programmed
> > and read back the same value. This has been working fine until the more
> > recent desktop/mobile platforms start enabling power gating for the PMC,
> > which prevents access to the counters. This results in the PMC support
> > being disabled unnecesarily.
> >
> > Unfortunatly, there is no documentation of since which generation
> > of hardware the original PMC HW bug was fixed. Although, it was fixed
> > soon after the first introduction of the PMC. Base on this, we assume
> > that the buggy platforms are less likely to be in used, and it should
> > be relatively safe to remove this legacy logic.
> >
> > Link: 
> > https://lore.kernel.org/linux-iommu/alpine.LNX.3.20.13.2006030935570.3181@xxxxxxxxxxxxxxxxxxxxxxx/ 
> >
> > Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=201753
> > Cc: Tj (Elloe Linux) <ml.linux@elloe.vision>
> > Cc: Shuah Khan <skhan@xxxxxxxxxxxxxxxxxxx>
> > Cc: Alexander Monakov <amonakov@xxxxxxxxx>
> > Cc: David Coe <david.coe@xxxxxxxxxx>
> > Cc: Paul Menzel <pmenzel@xxxxxxxxxxxxx>
> > Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
> > ---
>
>
> Tested-by: Shuah Khan <skhan@xxxxxxxxxxxxxxxxxxx>

Revert + this patch - same as my test on Ryzen 5

On AMD Ryzen 7 4700G with Radeon Graphics

These look real odd to me. Let me know if I should look further.

sudo ./perf stat -e 'amd_iommu_0/cmd_processed/, 
amd_iommu_0/cmd_processed_inv/, amd_iommu_0/ign_rd_wr_mmio_1ff8h/, 
amd_iommu_0/int_dte_hit/, amd_iommu_0/int_dte_mis/, 
amd_iommu_0/mem_dte_hit/, amd_iommu_0/mem_dte_mis/, 
amd_iommu_0/mem_iommu_tlb_pde_hit/, amd_iommu_0/mem_iommu_tlb_pde_mis/, 
amd_iommu_0/mem_iommu_tlb_pte_hit/, amd_iommu_0/mem_iommu_tlb_pte_mis/, 
amd_iommu_0/mem_pass_excl/, amd_iommu_0/mem_pass_pretrans/, 
amd_iommu_0/mem_pass_untrans/, amd_iommu_0/mem_target_abort/, 
amd_iommu_0/mem_trans_total/, amd_iommu_0/page_tbl_read_gst/, 
amd_iommu_0/page_tbl_read_nst/, amd_iommu_0/page_tbl_read_tot/, 
amd_iommu_0/smi_blk/, amd_iommu_0/smi_recv/, amd_iommu_0/tlb_inv/, 
amd_iommu_0/vapic_int_guest/, amd_iommu_0/vapic_int_non_guest/' sleep 10

 Performance counter stats for 'system wide':

17,761,952,514,865,374      amd_iommu_0/cmd_processed/ 
                   (33.28%)
18,582,155,570,607,472       amd_iommu_0/cmd_processed_inv/ 
                        (33.32%)
                 0       amd_iommu_0/ign_rd_wr_mmio_1ff8h/ 
                        (33.36%)
5,056,087,645,262,255       amd_iommu_0/int_dte_hit/ 
                 (33.40%)
32,831,106,446,308,888       amd_iommu_0/int_dte_mis/ 
                  (33.44%)
13,461,819,655,591,296       amd_iommu_0/mem_dte_hit/ 
                  (33.45%)
208,555,436,221,050,464       amd_iommu_0/mem_dte_mis/ 
                   (33.47%)
196,824,154,635,609,888       amd_iommu_0/mem_iommu_tlb_pde_hit/ 
                             (33.46%)
193,552,630,440,410,144       amd_iommu_0/mem_iommu_tlb_pde_mis/ 
                             (33.45%)
176,936,647,809,098,368       amd_iommu_0/mem_iommu_tlb_pte_hit/ 
                             (33.41%)
184,737,401,623,626,464       amd_iommu_0/mem_iommu_tlb_pte_mis/ 
                             (33.37%)
                 0       amd_iommu_0/mem_pass_excl/ 
                 (33.33%)
                 0       amd_iommu_0/mem_pass_pretrans/ 
                     (33.30%)
                 0       amd_iommu_0/mem_pass_untrans/ 
                    (33.28%)
                 0       amd_iommu_0/mem_target_abort/ 
                    (33.27%)
245,383,212,924,004,288       amd_iommu_0/mem_trans_total/ 
                       (33.27%)
                 0       amd_iommu_0/page_tbl_read_gst/ 
                     (33.28%)
262,267,045,917,967,264       amd_iommu_0/page_tbl_read_nst/ 
                         (33.27%)
256,308,216,913,137,600       amd_iommu_0/page_tbl_read_tot/ 
                         (33.28%)
                 0       amd_iommu_0/smi_blk/ 
               (33.27%)
                 0       amd_iommu_0/smi_recv/ 
               (33.27%)
                 0       amd_iommu_0/tlb_inv/ 
               (33.27%)
                 0       amd_iommu_0/vapic_int_guest/ 
                   (33.26%)
38,913,544,420,579,888       amd_iommu_0/vapic_int_non_guest/ 
                          (33.27%)

      10.003967760 seconds time elapsed

thanks,
-- Shuah