linux-kernel - Re: [PATCH 0/3] riscv: Add PARAVIRT

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Message-ID: <CAJF2gTSwR1OZQFJdPpq3gns=0M1vjHtL2Lpuy25dgmPsduREoA@mail.gmail.com>
Date: Tue, 24 Dec 2024 13:40:05 +0800
From: Guo Ren <guoren@...nel.org>
To: Andrew Jones <ajones@...tanamicro.com>
Cc: Anup Patel <anup@...infault.org>, paul.walmsley@...ive.com, palmer@...belt.com, 
	bjorn@...osinc.com, conor@...nel.org, leobras@...hat.com, 
	peterz@...radead.org, parri.andrea@...il.com, will@...nel.org, 
	longman@...hat.com, boqun.feng@...il.com, arnd@...db.de, 
	alexghiti@...osinc.com, rkrcmar@...tanamicro.com, 
	linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	Guo Ren <guoren@...ux.alibaba.com>
Subject: Re: [PATCH 0/3] riscv: Add PARAVIRT_SPINLOCKS support

On Tue, Dec 24, 2024 at 1:07 AM Andrew Jones <ajones@...tanamicro.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@...nel.org> wrote:
> > >
> > > From: Guo Ren <guoren@...ux.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