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

Atish Patra
2021-12-14T03:16:37Z

On Mon, Dec 13, 2021 at 5:52 PM Palmer Dabbelt <palmer@dabbelt.com> wrote:
>
> On Mon, 25 Oct 2021 12:53:39 PDT (-0700), Atish Patra 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.
>
> IMO we should keep it for a bit, so we have a transition period. These
> extensions are pretty new so we won't be able to count on everyone
> having them yet, this way we'll avoid breaking users.
>

Sure.

> This generally looks good, but I don't see any Acks from the perf
> maintainers. I'm happy to take this through the RISC-V tree, but I'd
> generally like to have at least an ack as perf isn't really my
> subsystem. MAINTAINERS seems to indicate that's Will and Mark, they're
> not To'd so maybe they just missed this?
>
> I fixed a few trivial checkpatch warnings, updated Atish's email

Thanks!

> address, and put this on palmer/riscv-pmu. Happy to hear any comments,

There was a comment from Jessica about needing a DT node in the kernel.
Here is the relevant discussion.

https://patchwork.kernel.org/project/linux-riscv/patch/20211025195350.242914-11-atish.patra@wdc.com/

To summarize, this series uses a PMU DT node to do the following things.

1. The PMU driver is DT probe based platform driver.
2. It uses the DT to discover the interrupt number
3. overflow will not be supported if the interrupt is not present in
the PMU DT node.

Jessica suggested that we should get rid of the DT node in the kernel because
1. The counter overflow interrupt is a fixed local interrupt number (0x13)
2. Overflow support should be enabled based on sscofpmf ISA extension
rather than interrupt property in
a DT node.

We did not have any discussion on the ISA extension discovery process
earlier. Thus, I did not add #2 in the current series.
Recently, it was briefly discussed and I am working on an
implementation based on that discussion.
Thus, I can address all the suggestions from Jessica in the next version.

I am okay with both approaches. Do you have any preference/suggestions
between the two approaches ?

> if nobody says anything then I'll just put that on riscv/for-next
> whenever I get back to my own email.
>

You may want to wait a little bit based on how the above discussion folds.

> > 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
>
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--
Regards,
Atish