Re: [v4 00/11] Improve RISC-V Perf support using SBI PMU and sscofpmf extension

Nikita Shubin
2021-12-14T09:21:03Z

Hello Atish!

I get linker error if CONFIG_RISCV_PMU_LEGACY is not set:

riscv64-unknown-linux-gnu-ld: drivers/perf/riscv_pmu_sbi.o: in function
`pmu_sbi_device_probe': linux/drivers/perf/riscv_pmu_sbi.c:688:
undefined reference to `riscv_pmu_legacy_init'

It looks like you need some guards or a dummy function for
riscv_pmu_legacy_init.

On Mon, 25 Oct 2021 12:53:39 -0700
Atish Patra <atish.patra@wdc.com> wrote:

> This series adds improved perf support for RISC-V based system using
> SBI PMU extension[1] and Sscofpmf extension[2]. The SBI PMU extension
> allows the kernel to program the counters for different events and
> start/stop counters while the sscofpmf extension allows the counter
> overflow interrupt and privilege mode filtering. An hardware platform
> can leverage SBI PMU extension without the sscofpmf extension if it
> supports mcountinhibit and mcounteren. However, the reverse is not
> true. With both of these extension enabled, a platform can take
> advantage of all both event counting and sampling using perf tool.
>
> This series introduces a platform perf driver instead of a existing
> arch specific implementation. The new perf implementation has adopted
> a modular approach where most of the generic event handling is done
> in the core library while individual PMUs need to only implement
> necessary features specific to the PMU. This is easily extensible and
> any future RISC-V PMU implementation can leverage this. Currently,
> SBI PMU driver & legacy PMU driver are implemented as a part of this
> series.
>
> The legacy driver tries to reimplement the existing minimal perf
> under a new config to maintain backward compatibility. This
> implementation only allows monitoring of always running
> cycle/instruction counters. Moreover, they can not be started or
> stopped. In general, this is very limited and not very useful. That's
> why, I am not very keen to carry the support into the new driver.
> However, I don't want to break perf for any existing hardware
> platforms. If everybody agrees that we don't need legacy perf
> implementation for older implementation, I will be happy to drop
> PATCH 4.
>
> This series has been tested in Qemu (RV64 & RV32) and HiFive
> Unmatched. Qemu[5] & OpenSBI [3] patches are required to test it on
> Qemu and a dt patch required in U-Boot[6] for HiFive Unmatched. Qemu
> changes are not backward compatible. That means, you can not use perf
> anymore on older Qemu versions with latest OpenSBI and/or Kernel.
> However, newer kernel will just use legacy pmu driver if old OpenSBI
> is detected.
>
> The U-Boot patch is just an example that encodes few of the events
> defined in fu740 documentation [7] in the DT. We can update the DT to
> include all the events defined if required.
>
> Here is an output of perf stat/report while running perf benchmark
> with OpenSBI, Linux kernel and U-Boot patches applied.
>
> HiFive Unmatched:
> =================
> perf stat -e cycles -e instructions -e L1-icache-load-misses -e
> branches -e branch-misses \ -e r0000000000000200 -e r0000000000000400
> \ -e r0000000000000800 perf bench sched messaging -g 25 -l 15
>
> # Running 'sched/messaging' benchmark:
> # 20 sender and receiver processes per group
> # 25 groups == 1000 processes run
>
> Total time: 0.826 [sec]
>
> Performance counter stats for 'perf bench sched messaging -g 25 -l
> 15':
>
> 3426710073 cycles (65.92%)
> 1348772808 instructions #0.39 insn per cycle
> (75.44%) 0 L1-icache-load-misses (72.28%)
> 201133996 branches (67.88%)
> 44663584 branch-misses #22.21% of all branches
> (35.01%) 248194747 r0000000000000200 (41.94%) --> Integer
> load instruction retired 156879950 r0000000000000400
> (43.58%) --> Integer store instruction retired 6988678
> r0000000000000800 (47.91%) --> Atomic memory operation retired
>
> 1.931335000 seconds time elapsed
>
> 1.100415000 seconds user
> 3.755176000 seconds sys
>
>
> QEMU:
> =========
> Perf stat:
> =========
>
> [root@fedora-riscv riscv]# perf stat -e r8000000000000005 -e
> r8000000000000007 \ -e r8000000000000006 -e r0000000000020002 -e
> r0000000000020004 -e branch-misses \ -e cache-misses -e
> dTLB-load-misses -e dTLB-store-misses -e iTLB-load-misses \ -e cycles
> -e instructions perf bench sched messaging -g 15 -l 10 \ Running with
> 15*40 (== 600) tasks. Time: 6.578
>
> Performance counter stats for './hackbench -pipe 15 process':
>
> 1,794 r8000000000000005 (52.59%) -->
> SBI_PMU_FW_SET_TIMER 2,859 r8000000000000007 (60.74%) -->
> SBI_PMU_FW_IPI_RECVD 4,205 r8000000000000006 (68.71%) -->
> SBI_PMU_FW_IPI_SENT 0 r0000000000020002 (81.69%)
> <not counted> r0000000000020004 (0.00%)
> <not counted> branch-misses (0.00%)
> <not counted> cache-misses (0.00%)
> 7,878,328 dTLB-load-misses (15.60%)
> 680,270 dTLB-store-misses (28.45%)
> 8,287,931 iTLB-load-misses (39.24%)
> 20,008,506,675 cycles (48.60%)
> 21,484,427,932 instructions # 1.07 insn per cycle (56.60%)
>
> 1.681344735 seconds time elapsed
>
> 0.614460000 seconds user
> 8.313254000 seconds sys
>
>
> Perf record:
> ============
> [root@fedora-riscv riscv]# perf record -e cycles -e instructions \
> -e dTLB-load-misses -e dTLB-store-misses -e iTLB-load-misses -c 10000
> \ perf bench sched messaging -g 15 -l 10
> # Running 'sched/messaging' benchmark:
> # 20 sender and receiver processes per group
> # 15 groups == 600 processes run
>
> Total time: 1.261 [sec]
> [ perf record: Woken up 1 times to write data ]
> [ perf record: Captured and wrote 0.101 MB perf.data (845 samples) ]
>
> [root@fedora-riscv riscv]# perf report
> Available samples
> 407 cycles
> _ 407 instructions
> _ 18 dTLB-load-misses
> _ 2 dTLB-store-misses
> _ 11 iTLB-load-misses
> _
> [1]
> https://github.com/riscv-non-isa/riscv-sbi-doc/blob/master/riscv-sbi.adoc
> [2]
> https://drive.google.com/file/d/171j4jFjIkKdj5LWcExphq4xG_2sihbfd/edit
> [3] https://github.com/atishp04/opensbi/tree/pmu_sscofpmf_v2 [4]
> https://github.com/atishp04/linux/tree/riscv_pmu_v4 [5]
> https://github.com/atishp04/qemu/tree/riscv_pmu_v3 [6]
> https://github.com/atishp04/u-boot/tree/hifive_unmatched_dt_pmu [7]
> https://sifive.cdn.prismic.io/sifive/de1491e5-077c-461d-9605-e8a0ce57337d_fu740-c000-manual-v1p3.pdf
>
> Changes from v3->v4:
> 1. Do not proceed overflow handler if event doesn't set for sampling.
> 2. overflow status register is only read after counters are stopped.
> 3. Added the PMU DT node for HiFive Unmatched.
>
> Changes from v2->v3:
> 1. Added interrupt overflow support.
> 2. Cleaned up legacy driver initialization.
> 3. Supports perf record now.
> 4. Added the DT binding and maintainers file.
> 5. Changed cpu hotplug notifier to be multi-state.
> 6. OpenSBI doesn't disable cycle/instret counter during boot. Update
> the perf code to disable all the counter during the boot.
>
> Changes from v1->v2
> 1. Implemented the latest SBI PMU extension specification.
> 2. The core platform driver was changed to operate as a library while
> only sbi based PMU is built as a driver. The legacy one is just a
> fallback if SBI PMU extension is not available.
>
> Atish Patra (11):
> RISC-V: Remove the current perf implementation
> RISC-V: Add CSR encodings for all HPMCOUNTERS
> RISC-V: Add a perf core library for pmu drivers
> RISC-V: Add a simple platform driver for RISC-V legacy perf
> RISC-V: Add RISC-V SBI PMU extension definitions
> dt-binding: pmu: Add RISC-V PMU DT bindings
> RISC-V: Add perf platform driver based on SBI PMU extension
> RISC-V: Add interrupt support for perf
> Documentation: riscv: Remove the old documentation
> riscv: dts: fu740: Add pmu node
> MAINTAINERS: Add entry for RISC-V PMU drivers
>
> .../devicetree/bindings/perf/riscv,pmu.yaml | 51 ++
> Documentation/riscv/pmu.rst | 255 ------
> MAINTAINERS | 10 +
> arch/riscv/Kconfig | 13 -
> arch/riscv/boot/dts/sifive/fu740-c000.dtsi | 3 +
> arch/riscv/include/asm/csr.h | 66 +-
> arch/riscv/include/asm/perf_event.h | 72 --
> arch/riscv/include/asm/sbi.h | 97 +++
> arch/riscv/kernel/Makefile | 1 -
> arch/riscv/kernel/perf_event.c | 485 ------------
> drivers/perf/Kconfig | 25 +
> drivers/perf/Makefile | 5 +
> drivers/perf/riscv_pmu.c | 331 ++++++++
> drivers/perf/riscv_pmu_legacy.c | 143 ++++
> drivers/perf/riscv_pmu_sbi.c | 732 ++++++++++++++++++
> include/linux/cpuhotplug.h | 1 +
> include/linux/perf/riscv_pmu.h | 69 ++
> 17 files changed, 1532 insertions(+), 827 deletions(-)
> create mode 100644
> Documentation/devicetree/bindings/perf/riscv,pmu.yaml delete mode
> 100644 Documentation/riscv/pmu.rst delete mode 100644
> arch/riscv/kernel/perf_event.c create mode 100644
> drivers/perf/riscv_pmu.c create mode 100644
> drivers/perf/riscv_pmu_legacy.c create mode 100644
> drivers/perf/riscv_pmu_sbi.c create mode 100644
> include/linux/perf/riscv_pmu.h
>
> --
> 2.31.1
>
>
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