linux-kernel - Re: [PATCH 2/5] riscv: Add QUEUED_SPINLOCKS & QUEUED

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Date:   Wed, 25 Nov 2020 08:52:23 +0800
From:   Guo Ren <guoren@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Palmer Dabbelt <palmerdabbelt@...gle.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Anup Patel <anup@...infault.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-csky@...r.kernel.org, Guo Ren <guoren@...ux.alibaba.com>,
        Michael Clark <michaeljclark@....com>
Subject: Re: [PATCH 2/5] riscv: Add QUEUED_SPINLOCKS & QUEUED_RWLOCKS supported

Thx Peter,

On Tue, Nov 24, 2020 at 10:39 PM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Tue, Nov 24, 2020 at 01:43:54PM +0000, guoren@...nel.org wrote:
> > diff --git a/arch/riscv/include/asm/Kbuild b/arch/riscv/include/asm/Kbuild
> > index 59dd7be..6f5f438 100644
> > --- a/arch/riscv/include/asm/Kbuild
> > +++ b/arch/riscv/include/asm/Kbuild
> > @@ -6,3 +6,6 @@ generic-y += kvm_para.h
> >  generic-y += local64.h
> >  generic-y += user.h
> >  generic-y += vmlinux.lds.h
> > +generic-y += mcs_spinlock.h
> > +generic-y += qrwlock.h
> > +generic-y += qspinlock.h
> > diff --git a/arch/riscv/include/asm/cmpxchg.h b/arch/riscv/include/asm/cmpxchg.h
> > index 5609185..e178700 100644
> > --- a/arch/riscv/include/asm/cmpxchg.h
> > +++ b/arch/riscv/include/asm/cmpxchg.h
> > @@ -16,7 +16,43 @@
> >       __typeof__(ptr) __ptr = (ptr);                                  \
> >       __typeof__(new) __new = (new);                                  \
> >       __typeof__(*(ptr)) __ret;                                       \
> > +     register unsigned long __rc, tmp, align, addr;                  \
> >       switch (size) {                                                 \
> > +     case 2:                                                         \
> > +             align = ((unsigned long) __ptr & 0x3);                  \
> > +             addr = ((unsigned long) __ptr & ~0x3);                  \
> > +             if (align) {                                            \
> > +             __asm__ __volatile__ (                                  \
> > +                     "0:     lr.w %0, 0(%z4)\n"                      \
> > +                     "       move %1, %0\n"                          \
> > +                     "       slli %1, %1, 16\n"                      \
> > +                     "       srli %1, %1, 16\n"                      \
> > +                     "       move %2, %z3\n"                         \
> > +                     "       slli %2, %2, 16\n"                      \
> > +                     "       or   %1, %2, %1\n"                      \
> > +                     "       sc.w %2, %1, 0(%z4)\n"                  \
> > +                     "       bnez %2, 0b\n"                          \
> > +                     "       srli %0, %0, 16\n"                      \
> > +                     : "=&r" (__ret), "=&r" (tmp), "=&r" (__rc)      \
> > +                     : "rJ" (__new), "rJ"(addr)                      \
> > +                     : "memory");                                    \
> > +             } else {                                                \
> > +             __asm__ __volatile__ (                                  \
> > +                     "0:     lr.w %0, (%z4)\n"                       \
> > +                     "       move %1, %0\n"                          \
> > +                     "       srli %1, %1, 16\n"                      \
> > +                     "       slli %1, %1, 16\n"                      \
> > +                     "       move %2, %z3\n"                         \
> > +                     "       or   %1, %2, %1\n"                      \
> > +                     "       sc.w %2, %1, 0(%z4)\n"                  \
> > +                     "       bnez %2, 0b\n"                          \
> > +                     "       slli %0, %0, 16\n"                      \
> > +                     "       srli %0, %0, 16\n"                      \
> > +                     : "=&r" (__ret), "=&r" (tmp), "=&r" (__rc)      \
> > +                     : "rJ" (__new), "rJ"(addr)                      \
> > +                     : "memory");                                    \
> > +             }                                                       \
> > +             break;                                                  \
> >       case 4:                                                         \
> >               __asm__ __volatile__ (                                  \
> >                       "       amoswap.w %0, %2, %1\n"                 \
>
> I'm pretty sure there's a handfull of implementations like this out
> there... if only we could share.
Michael has sent qspinlock before, ref to Link below. He reused mips' code.

Link: https://lore.kernel.org/linux-riscv/20190211043829.30096-1-michaeljclark@mac.com/

Which short xchg implementation do you prefer (Mine or his)?

>
> Anyway, this too should be an independent patch.
Ok, I'll separate it into two patches,
1. implement short xchg
2. qspinlock enabled based on Michael's patch

-- 
Best Regards
 Guo Ren

ML: https://lore.kernel.org/linux-csky/