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Message-ID: <20241223-165e7b7ee58e2dede8bfd830@orel>
Date: Mon, 23 Dec 2024 18:07:26 +0100
From: Andrew Jones <ajones@...tanamicro.com>
To: Anup Patel <anup@...infault.org>
Cc: guoren@...nel.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 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.
>
> Please work with the PRS TG and Hypervisors SIG for the proposed
> SBI extension.
>
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
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