[RFC PATCH V2 0/4] RISC-V: Add PARAVIRT_SPINLOCKS support

guoren
2024-12-27T01:10:45Z

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/

Changes in v2:
- Add RFC tag.
- Using new SBI_EXT_PVLOCK ID.
- Add virt_spin_lock support.
- Add nopvspin support.

Guo Ren (4):
RISC-V: paravirt: Add pvqspinlock KVM backend
RISC-V: paravirt: Add pvqspinlock frontend
RISC-V: paravirt: pvqspinlock: Add trace point for pv_kick/wait
RISC-V: paravirt: Enable virt_spin_lock() when disable
PARAVIRT_SPINLOCKS

.../admin-guide/kernel-parameters.txt | 2 +-
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 | 59 ++++++++++++++
arch/riscv/include/asm/qspinlock_paravirt.h | 28 +++++++
arch/riscv/include/asm/sbi.h | 21 +++++
arch/riscv/include/uapi/asm/kvm.h | 1 +
arch/riscv/kernel/Makefile | 1 +
arch/riscv/kernel/qspinlock_paravirt.c | 77 +++++++++++++++++++
arch/riscv/kernel/sbi.c | 2 +-
arch/riscv/kernel/setup.c | 33 ++++++++
.../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 ++++++++++++++
16 files changed, 357 insertions(+), 3 deletions(-)
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