[ RFC 0/6] Improve PMU support

[Atish Patra]

The latest version of the SBI specification includes a Performance Monitoring
Unit(PMU) extension[1] which allows the supervisor to start/stop/configure
various PMU events. This series implements basic infrastructure to support
PMU in virt machine. Qemu can support only cycle and instruction counters.
Thus, this series adds only those two events. However, it enables all
the counters and adds all the necessary checks required before accessing
a counter. This will allow us to add any other PMU events in future.

First patch in this series is just a cleanup while PATCH 2-5 adds support
for all the PMU CSR. PATCH 6 adds a DT node as per DT bindings defined in
OpenSBI[2]. PATCH 7 is just a debug patch and is not supposed to be merged.

Here is an output of perf stat while running hackbench with OpenSBI & Linux
kernel patches applied [3].

[root@fedora-riscv riscv]# perf stat -e r8000000000000007 -e r8000000000000006 \
-e r0000000000000002 -e r0000000000000004 -e branch-misses -e cache-misses \
-e cycles -e instructions ./hackbench -pipe 15 process 15

Running with 15*40 (== 600) tasks.
Time: 1.548

 Performance counter stats for './hackbench -pipe 15 process 15':

             7,103      r8000000000000007     (62.56%) --> SBI_PMU_FW_IPI_RECVD
             7,767      r8000000000000006     (12.19%) --> SBI_PMU_FW_IPI_SENT
                 0      r0000000000000002     (24.79%) --> a custom raw event 
described in DT
     <not counted>      r0000000000000004     (0.00%)  --> non-supported raw 
event described in DT
                 0      branch-misses         (12.65%) 
                 0      cache-misses          (25.36%)
    27,978,868,702      cycles                (38.12%)
    27,849,527,556      instructions          # 1.00  insn per cycle  (50.46%)

       2.431195184 seconds time elapsed

       1.553153000 seconds user
      13.615924000 seconds sys

The patches can also be found in the github[4].

[1] https://lists.riscv.org/g/tech-unixplatformspec/message/598
[2] https://github.com/atishp04/opensbi/tree/riscv_pmu_v1 
[3] https://github.com/atishp04/linux/tree/riscv_pmu_v1 
[4] https://github.com/atishp04/qemu/tree/riscv_pmu_v1 

Atish Patra (6):
target/riscv: Remove privilege v1.9 specific CSR related code
target/riscv: Implement mcountinhibit CSR
target/riscv: Support mcycle/minstret write operation
target/riscv: Add support for hpmcounters/hpmevents
hw/riscv: virt: Add PMU device tree node to support SBI PMU extension
hw/riscv: virt: DEBUG PATCH to test PMU

hw/riscv/virt.c           |  52 +++-
target/riscv/cpu.c        |   2 +-
target/riscv/cpu.h        |  21 +-
target/riscv/cpu_bits.h   |  27 +-
target/riscv/cpu_helper.c |  12 +-
target/riscv/csr.c        | 601 ++++++++++++++++++++++++++------------
target/riscv/machine.c    |  12 +-
target/riscv/translate.c  |   4 +-
8 files changed, 499 insertions(+), 232 deletions(-)

--
2.25.1