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

Hi Palmer,

On Mon, Apr 22, 2024 at 3:29 PM Anup Patel anup@brainfault.org wrote:

On Sat, Apr 20, 2024 at 5:17 AM Atish Patra atishp@rivosinc.com 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.

Please use the kvm-riscv-for-palmer-6.10 tag in the KVM RISC-V repo (https://github.com/kvm-riscv/linux.git) as a shared tag for the upcoming Linux-6.10 merge window.

This tag is based on Linux-6.9-rc3.

Regards, Anup

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

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