[PATCH 0/3] riscv: Add PARAVIRT_SPINLOCKS support

[guoren at kernel.org]

From: Guo Ren <guoren at linux.alibaba.com>

Paravirtualized spinlocks allow a unfair qspinlock to replace the
ticket-lock or native fair qspinlock implementation with something
virtualization-friendly, for example, halt the virtual CPU rather
than spinning.

You could observe the paravirt qspinlock internal work situation with
/sys/kernel/debug/tracing/trace:

ls /sys/kernel/debug/tracing/events/paravirt/
 enable   filter   pv_kick  pv_wait

echo 1 > /sys/kernel/debug/tracing/events/paravirt/enable
cat /sys/kernel/debug/tracing/trace
 entries-in-buffer/entries-written: 33927/33927   #P:12

                                _-----=> irqs-off/BH-disabled
                               / _----=> need-resched
                              | / _---=> hardirq/softirq
                              || / _--=> preempt-depth
                              ||| / _-=> migrate-disable
                              |||| /     delay
           TASK-PID     CPU#  |||||  TIMESTAMP  FUNCTION
              | |         |   |||||     |         |
             sh-100     [001] d..2.    28.312294: pv_wait: cpu 1 out of wfi
         <idle>-0       [000] d.h4.    28.322030: pv_kick: cpu 0 kick target cpu 1
             sh-100     [001] d..2.    30.982631: pv_wait: cpu 1 out of wfi
         <idle>-0       [000] d.h4.    30.993289: pv_kick: cpu 0 kick target cpu 1
             sh-100     [002] d..2.    44.987573: pv_wait: cpu 2 out of wfi
         <idle>-0       [000] d.h4.    44.989000: pv_kick: cpu 0 kick target cpu 2
         <idle>-0       [003] d.s3.    51.593978: pv_kick: cpu 3 kick target cpu 4
      rcu_sched-15      [004] d..2.    51.595192: pv_wait: cpu 4 out of wfi
lock_torture_wr-115     [004] ...2.    52.656482: pv_kick: cpu 4 kick target cpu 2
lock_torture_wr-113     [002] d..2.    52.659146: pv_wait: cpu 2 out of wfi
lock_torture_wr-114     [008] d..2.    52.659507: pv_wait: cpu 8 out of wfi
lock_torture_wr-114     [008] d..2.    52.663503: pv_wait: cpu 8 out of wfi
lock_torture_wr-113     [002] ...2.    52.666128: pv_kick: cpu 2 kick target cpu 8
lock_torture_wr-114     [008] d..2.    52.667261: pv_wait: cpu 8 out of wfi
lock_torture_wr-114     [009] .n.2.    53.141515: pv_kick: cpu 9 kick target cpu 11
lock_torture_wr-113     [002] d..2.    53.143339: pv_wait: cpu 2 out of wfi
lock_torture_wr-116     [007] d..2.    53.143412: pv_wait: cpu 7 out of wfi
lock_torture_wr-118     [000] d..2.    53.143457: pv_wait: cpu 0 out of wfi
lock_torture_wr-115     [008] d..2.    53.143481: pv_wait: cpu 8 out of wfi
lock_torture_wr-117     [011] d..2.    53.143522: pv_wait: cpu 11 out of wfi
lock_torture_wr-117     [011] ...2.    53.143987: pv_kick: cpu 11 kick target cpu 8
lock_torture_wr-115     [008] ...2.    53.144269: pv_kick: cpu 8 kick target cpu 7

This series is split from [1].

[1]: https://lore.kernel.org/linux-riscv/20231225125847.2778638-1-guoren@kernel.org/

Guo Ren (3):
  RISC-V: paravirt: Add pvqspinlock KVM backend
  RISC-V: paravirt: Add pvqspinlock frontend
  RISC-V: paravirt: pvqspinlock: Add trace point for pv_kick/wait

 arch/riscv/Kconfig                            | 12 +++
 arch/riscv/include/asm/Kbuild                 |  1 -
 arch/riscv/include/asm/kvm_vcpu_sbi.h         |  1 +
 arch/riscv/include/asm/qspinlock.h            | 35 +++++++++
 arch/riscv/include/asm/qspinlock_paravirt.h   | 28 +++++++
 arch/riscv/include/asm/sbi.h                  |  5 ++
 arch/riscv/include/uapi/asm/kvm.h             |  1 +
 arch/riscv/kernel/Makefile                    |  1 +
 arch/riscv/kernel/qspinlock_paravirt.c        | 74 +++++++++++++++++++
 arch/riscv/kernel/setup.c                     |  4 +
 .../kernel/trace_events_filter_paravirt.h     | 60 +++++++++++++++
 arch/riscv/kvm/Makefile                       |  1 +
 arch/riscv/kvm/vcpu_sbi.c                     |  4 +
 arch/riscv/kvm/vcpu_sbi_pvlock.c              | 57 ++++++++++++++
 14 files changed, 283 insertions(+), 1 deletion(-)
 create mode 100644 arch/riscv/include/asm/qspinlock.h
 create mode 100644 arch/riscv/include/asm/qspinlock_paravirt.h
 create mode 100644 arch/riscv/kernel/qspinlock_paravirt.c
 create mode 100644 arch/riscv/kernel/trace_events_filter_paravirt.h
 create mode 100644 arch/riscv/kvm/vcpu_sbi_pvlock.c

-- 
2.40.1