Messages in this thread | | | Subject | Re: [PATCH 2/2] iommu/amd: Remove performance counter pre-initialization test | From | Shuah Khan <> | Date | Fri, 9 Apr 2021 14:00:34 -0600 |
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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@monopod.intra.ispras.ru/ > Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=201753 > Cc: Tj (Elloe Linux) <ml.linux@elloe.vision> > Cc: Shuah Khan <skhan@linuxfoundation.org> > Cc: Alexander Monakov <amonakov@ispras.ru> > Cc: David Coe <david.coe@live.co.uk> > Cc: Paul Menzel <pmenzel@molgen.mpg.de> > Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com> > ---
Tested-by: Shuah Khan <skhan@linuxfoundation.org>
thanks, -- Shuah
Results with this patch on AMD Ryzen 5 PRO 2400GE w/ Radeon Vega Graphics
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':
156 amd_iommu_0/cmd_processed/ (33.30%) 80 amd_iommu_0/cmd_processed_inv/ (33.38%) 0 amd_iommu_0/ign_rd_wr_mmio_1ff8h/ (33.40%) 0 amd_iommu_0/int_dte_hit/ (33.43%) 325 amd_iommu_0/int_dte_mis/ (33.44%) 1,951 amd_iommu_0/mem_dte_hit/ (33.45%) 7,589 amd_iommu_0/mem_dte_mis/ (33.49%) 325 amd_iommu_0/mem_iommu_tlb_pde_hit/ (33.45%) 2,460 amd_iommu_0/mem_iommu_tlb_pde_mis/ (33.41%) 2,510 amd_iommu_0/mem_iommu_tlb_pte_hit/ (33.38%) 5,526 amd_iommu_0/mem_iommu_tlb_pte_mis/ (33.33%) 0 amd_iommu_0/mem_pass_excl/ (33.29%) 0 amd_iommu_0/mem_pass_pretrans/ (33.28%) 1,556 amd_iommu_0/mem_pass_untrans/ (33.27%) 0 amd_iommu_0/mem_target_abort/ (33.26%) 3,112 amd_iommu_0/mem_trans_total/ (33.29%) 0 amd_iommu_0/page_tbl_read_gst/ (33.29%) 1,813 amd_iommu_0/page_tbl_read_nst/ (33.25%) 2,242 amd_iommu_0/page_tbl_read_tot/ (33.27%) 0 amd_iommu_0/smi_blk/ (33.29%) 0 amd_iommu_0/smi_recv/ (33.28%) 0 amd_iommu_0/tlb_inv/ (33.28%) 0 amd_iommu_0/vapic_int_guest/ (33.25%) 0 amd_iommu_0/vapic_int_non_guest/ (33.26%)
10.003200316 seconds time elapsed
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