Re: [PATCH v8 00/24] RISC-V SBI v2.0 PMU improvements and Perf sampling in KVM guest

[Anup Patel]

On Sat, Apr 20, 2024 at 5:17 AM Atish Patra <atishp@xxxxxxxxxxxx> wrote:
>
> This series implements SBI PMU improvements done in SBI v2.0[1] i.e. PMU snapshot
> and fw_read_hi() functions.
>
> SBI v2.0 introduced PMU snapshot feature which allows the SBI implementation
> to provide counter information (i.e. values/overflow status) via a shared
> memory between the SBI implementation and supervisor OS. This allows to minimize
> the number of traps in when perf being used inside a kvm guest as it relies on
> SBI PMU + trap/emulation of the counters.
>
> The current set of ratified RISC-V specification also doesn't allow scountovf
> to be trap/emulated by the hypervisor. The SBI PMU snapshot bridges the gap
> in ISA as well and enables perf sampling in the guest. However, LCOFI in the
> guest only works via IRQ filtering in AIA specification. That's why, AIA
> has to be enabled in the hardware (at least the Ssaia extension) in order to
> use the sampling support in the perf.
>
> Here are the patch wise implementation details.
>
> PATCH 1,4,7,8,9,10,11,15 : Generic cleanups/improvements.
> PATCH 2,3,14 : FW_READ_HI function implementation
> PATCH 5-6: Add PMU snapshot feature in sbi pmu driver
> PATCH 12-13: KVM implementation for snapshot and sampling in kvm guests
> PATCH 16-17: Generic improvements for kvm selftests
> PATCH 18-22: KVM selftests for SBI PMU extension
>
> The series is based on v6.9-rc4 and is available at:
>
> https://github.com/atishp04/linux/tree/kvm_pmu_snapshot_v8
>
> The kvmtool patch is also available at:
> https://github.com/atishp04/kvmtool/tree/sscofpmf
>
> It also requires Ssaia ISA extension to be present in the hardware in order to
> get perf sampling support in the guest. In Qemu virt machine, it can be done
> by the following config.
>
> ```
> -cpu rv64,sscofpmf=true,x-ssaia=true
> ```
>
> There is no other dependencies on AIA apart from that. Thus, Ssaia must be disabled
> for the guest if AIA patches are not available. Here is the example command.
>
> ```
> ./lkvm-static run -m 256 -c2 --console serial -p "console=ttyS0 earlycon" --disable-ssaia -k ./Image --debug
> ```
>
> The series has been tested only in Qemu.
> Here is the snippet of the perf running inside a kvm guest.
>
> ===================================================
> $ perf record -e cycles -e instructions perf bench sched messaging -g 5
> ...
> $ Running 'sched/messaging' benchmark:
> ...
> [   45.928723] perf_duration_warn: 2 callbacks suppressed
> [   45.929000] perf: interrupt took too long (484426 > 483186), lowering kernel.perf_event_max_sample_rate to 250
> $ 20 sender and receiver processes per group
> $ 5 groups == 200 processes run
>
>      Total time: 14.220 [sec]
> [ perf record: Woken up 1 times to write data ]
> [ perf record: Captured and wrote 0.117 MB perf.data (1942 samples) ]
> $ perf report --stdio
> $ To display the perf.data header info, please use --header/--header-only optio>
> $
> $
> $ Total Lost Samples: 0
> $
> $ Samples: 943  of event 'cycles'
> $ Event count (approx.): 5128976844
> $
> $ Overhead  Command          Shared Object                Symbol               >
> $ ........  ...............  ...........................  ....................>
> $
>      7.59%  sched-messaging  [kernel.kallsyms]            [k] memcpy
>      5.48%  sched-messaging  [kernel.kallsyms]            [k] percpu_counter_ad>
>      5.24%  sched-messaging  [kernel.kallsyms]            [k] __sbi_rfence_v02_>
>      4.00%  sched-messaging  [kernel.kallsyms]            [k] _raw_spin_unlock_>
>      3.79%  sched-messaging  [kernel.kallsyms]            [k] set_pte_range
>      3.72%  sched-messaging  [kernel.kallsyms]            [k] next_uptodate_fol>
>      3.46%  sched-messaging  [kernel.kallsyms]            [k] filemap_map_pages
>      3.31%  sched-messaging  [kernel.kallsyms]            [k] handle_mm_fault
>      3.20%  sched-messaging  [kernel.kallsyms]            [k] finish_task_switc>
>      3.16%  sched-messaging  [kernel.kallsyms]            [k] clear_page
>      3.03%  sched-messaging  [kernel.kallsyms]            [k] mtree_range_walk
>      2.42%  sched-messaging  [kernel.kallsyms]            [k] flush_icache_pte
>
> ===================================================
>
> [1] https://github.com/riscv-non-isa/riscv-sbi-doc
>
> Changes from v7->v8:
> 1. Updated event states so that shared memory is updated only during stop
>    operations.
> 2. Avoid clobbering lower XLEN counter/overflow values in shared memory
>    by maintaining a temporary copy for RV32.
> 3. Improved overflow handling in snapshot case by supporting all 64 values.
> 4. Minor cleanups based on suggestions on v7.
>
> Changes from v6->v7:
> 1. Used SBI_SHMEM_DISABLE in the driver.
> 2. Added RB Tags.
> 3. Improved the sbi_pmu_test commandline to allow disabling multiple
>    tests.
>
> Changes from v5->v6:
> 1. Added a patch for command line option for the sbi pmu tests.
> 2. Removed redundant prints and restructure the code little bit.
> 3. Added a patch for computing the sbi minor version correctly.
> 4. Addressed all other comments on v5.
>
> Changes from v4->v5:
> 1. Moved sbi related definitions to its own header file from processor.h
> 2. Added few helper functions for selftests.
> 3. Improved firmware counter read and RV32 start/stop functions.
> 4. Converted all the shifting operations to use BIT macro
> 5. Addressed all other comments on v4.
>
> Changes from v3->v4:
> 1. Added selftests.
> 2. Fixed an issue to clear the interrupt pending bits.
> 3. Fixed the counter index in snapshot memory start function.
>
> Changes from v2->v3:
> 1. Fixed a patchwork warning on patch6.
> 2. Fixed a comment formatting & nit fix in PATCH 3 & 5.
> 3. Moved the hvien update and sscofpmf enabling to PATCH 9 from PATCH 8.
>
> Changes from v1->v2:
> 1. Fixed warning/errors from patchwork CI.
> 2. Rebased on top of kvm-next.
> 3. Added Acked-by tags.
>
> Changes from RFC->v1:
> 1. Addressed all the comments on RFC series.
> 2. Removed PATCH2 and merged into later patches.
> 3. Added 2 more patches for minor fixes.
> 4. Fixed KVM boot issue without Ssaia and made sscofpmf in guest dependent on
>    Ssaia in the host.
>
> Atish Patra (24):
> RISC-V: Fix the typo in Scountovf CSR name
> RISC-V: Add FIRMWARE_READ_HI definition
> drivers/perf: riscv: Read upper bits of a firmware counter
> drivers/perf: riscv: Use BIT macro for shifting operations
> RISC-V: Add SBI PMU snapshot definitions
> RISC-V: KVM: Rename the SBI_STA_SHMEM_DISABLE to a generic name
> RISC-V: Use the minor version mask while computing sbi version
> drivers/perf: riscv: Fix counter mask iteration for RV32
> drivers/perf: riscv: Implement SBI PMU snapshot function
> RISC-V: KVM: Fix the initial sample period value
> RISC-V: KVM: No need to update the counter value during reset
> RISC-V: KVM: No need to exit to the user space if perf event failed
> RISC-V: KVM: Implement SBI PMU Snapshot feature
> RISC-V: KVM: Add perf sampling support for guests
> RISC-V: KVM: Support 64 bit firmware counters on RV32
> RISC-V: KVM: Improve firmware counter read function
> KVM: riscv: selftests: Move sbi definitions to its own header file
> KVM: riscv: selftests: Add helper functions for extension checks
> KVM: riscv: selftests: Add Sscofpmf to get-reg-list test
> KVM: riscv: selftests: Add SBI PMU extension definitions
> KVM: riscv: selftests: Add SBI PMU selftest
> KVM: riscv: selftests: Add a test for PMU snapshot functionality
> KVM: riscv: selftests: Add a test for counter overflow
> KVM: riscv: selftests: Add commandline option for SBI PMU test

Queued this series for Linux-6.10

If new issues are discovered then send patches based on
the KVM riscv queue.

Thanks,
Anup

>
> arch/riscv/include/asm/csr.h                  |   5 +-
> arch/riscv/include/asm/kvm_vcpu_pmu.h         |  16 +-
> arch/riscv/include/asm/sbi.h                  |  38 +-
> arch/riscv/include/uapi/asm/kvm.h             |   1 +
> arch/riscv/kernel/paravirt.c                  |   6 +-
> arch/riscv/kvm/aia.c                          |   5 +
> arch/riscv/kvm/vcpu.c                         |  15 +-
> arch/riscv/kvm/vcpu_onereg.c                  |   6 +
> arch/riscv/kvm/vcpu_pmu.c                     | 260 ++++++-
> arch/riscv/kvm/vcpu_sbi_pmu.c                 |  17 +-
> arch/riscv/kvm/vcpu_sbi_sta.c                 |   4 +-
> drivers/perf/riscv_pmu.c                      |   1 +
> drivers/perf/riscv_pmu_sbi.c                  | 309 +++++++-
> include/linux/perf/riscv_pmu.h                |   6 +
> tools/testing/selftests/kvm/Makefile          |   1 +
> .../selftests/kvm/include/riscv/processor.h   |  49 +-
> .../testing/selftests/kvm/include/riscv/sbi.h | 141 ++++
> .../selftests/kvm/include/riscv/ucall.h       |   1 +
> .../selftests/kvm/lib/riscv/processor.c       |  12 +
> .../testing/selftests/kvm/riscv/arch_timer.c  |   2 +-
> .../selftests/kvm/riscv/get-reg-list.c        |   4 +
> .../selftests/kvm/riscv/sbi_pmu_test.c        | 681 ++++++++++++++++++
> tools/testing/selftests/kvm/steal_time.c      |   4 +-
> 23 files changed, 1467 insertions(+), 117 deletions(-)
> create mode 100644 tools/testing/selftests/kvm/include/riscv/sbi.h
> create mode 100644 tools/testing/selftests/kvm/riscv/sbi_pmu_test.c
>
> --
> 2.34.1
>