Re: [PATCH 0/3] riscv: Add PARAVIRT_SPINLOCKS support

Guo Ren
2024-12-24T05:40:39Z

On Tue, Dec 24, 2024 at 1:07 AM Andrew Jones <ajones@ventanamicro.com> wrote:
>
> On Mon, Dec 23, 2024 at 01:44:50PM +0530, Anup Patel wrote:
> > On Sun, Dec 22, 2024 at 9:09 AM <guoren@kernel.org> wrote:
> > >
> > > From: Guo Ren <guoren@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
> >
> > This should be an RFC series until the corresponding SBI extension
> > is frozen. AFAIK, no one has posted any SBI extension in this context
> > on any of the RVI mailing lists.
Oh, I forgot the RFC tag. Thanks for reminding me.

> >
> > Please work with the PRS TG and Hypervisors SIG for the proposed
> > SBI extension.
Yes, I will.

> >
>
> I promised Guo I'd help out by writing a draft for the SBI extension. I'll
> try to get something posted this week.
Thanks, drew.

--
Best Regards
Guo Ren