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References: <20220318083421.2062259-1-guoren@kernel.org> <mhng-88509dbf-71a1-495a-84a7-3dffef8c77a5@palmer-ri-x1c9>
In-Reply-To: <mhng-88509dbf-71a1-495a-84a7-3dffef8c77a5@palmer-ri-x1c9>
From:   Guo Ren <guoren@kernel.org>
Date:   Sat, 19 Mar 2022 12:01:49 +0800
Message-ID: <CAJF2gTShUjTQ=7g3uW8JmPzkZSG0fWKK7fXgAsERSUfrCgzA0w@mail.gmail.com>
Subject: Re: [PATCH] csky: Move to generic ticket-spinlock
To:     Palmer Dabbelt <palmer@rivosinc.com>
Cc:     linux-csky@vger.kernel.org,
        linux-arch <linux-arch@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Guo Ren <guoren@linux.alibaba.com>
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Hi Palmer,

On Sat, Mar 19, 2022 at 6:48 AM Palmer Dabbelt <palmer@rivosinc.com> wrote:
>
> On Fri, 18 Mar 2022 01:34:21 PDT (-0700), guoren@kernel.org wrote:
> > From: Guo Ren <guoren@linux.alibaba.com>
> >
> > There is no benefit from custom implementation for ticket-spinlock,
> > so move to generic ticket-spinlock for easy maintenance.
> >
> > Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
> > Cc: Palmer Dabbelt <palmer@rivosinc.com>
>
> Thanks, one less port to look at ;)
>
> Looks like there were a few comments on the v1, and I wasn't going to
> target this at the upcoming merge window anyway because I wanted to give
Agree, we needn't so hurry.

> the various RISC-V vendors time to test stuff.  LMK if you want me to
> add this to the others, but I was planning on posting a stable tag
> either way so no big deal on my end.
Yes, I hope csky's could be in the series. And I updated V2 with
Arnd's suggestion, please have a look:
https://lore.kernel.org/linux-arch/20220319035457.2214979-1-guoren@kernel.org/T/#t

>
> > ---
> >  arch/csky/include/asm/Kbuild           |  2 +
> >  arch/csky/include/asm/spinlock.h       | 82 +-------------------------
> >  arch/csky/include/asm/spinlock_types.h | 20 +------
> >  3 files changed, 4 insertions(+), 100 deletions(-)
> >
> > diff --git a/arch/csky/include/asm/Kbuild b/arch/csky/include/asm/Kbuild
> > index 904a18a818be..d94434288c31 100644
> > --- a/arch/csky/include/asm/Kbuild
> > +++ b/arch/csky/include/asm/Kbuild
> > @@ -3,6 +3,8 @@ generic-y += asm-offsets.h
> >  generic-y += extable.h
> >  generic-y += gpio.h
> >  generic-y += kvm_para.h
> > +generic-y += ticket-lock.h
> > +generic-y += ticket-lock-types.h
> >  generic-y += qrwlock.h
> >  generic-y += user.h
> >  generic-y += vmlinux.lds.h
> > diff --git a/arch/csky/include/asm/spinlock.h b/arch/csky/include/asm/spinlock.h
> > index 69f5aa249c5f..8bc179ba0d8d 100644
> > --- a/arch/csky/include/asm/spinlock.h
> > +++ b/arch/csky/include/asm/spinlock.h
> > @@ -3,87 +3,7 @@
> >  #ifndef __ASM_CSKY_SPINLOCK_H
> >  #define __ASM_CSKY_SPINLOCK_H
> >
> > -#include <linux/spinlock_types.h>
> > -#include <asm/barrier.h>
> > -
> > -/*
> > - * Ticket-based spin-locking.
> > - */
> > -static inline void arch_spin_lock(arch_spinlock_t *lock)
> > -{
> > -     arch_spinlock_t lockval;
> > -     u32 ticket_next = 1 << TICKET_NEXT;
> > -     u32 *p = &lock->lock;
> > -     u32 tmp;
> > -
> > -     asm volatile (
> > -             "1:     ldex.w          %0, (%2) \n"
> > -             "       mov             %1, %0   \n"
> > -             "       add             %0, %3   \n"
> > -             "       stex.w          %0, (%2) \n"
> > -             "       bez             %0, 1b   \n"
> > -             : "=&r" (tmp), "=&r" (lockval)
> > -             : "r"(p), "r"(ticket_next)
> > -             : "cc");
> > -
> > -     while (lockval.tickets.next != lockval.tickets.owner)
> > -             lockval.tickets.owner = READ_ONCE(lock->tickets.owner);
> > -
> > -     smp_mb();
> > -}
> > -
> > -static inline int arch_spin_trylock(arch_spinlock_t *lock)
> > -{
> > -     u32 tmp, contended, res;
> > -     u32 ticket_next = 1 << TICKET_NEXT;
> > -     u32 *p = &lock->lock;
> > -
> > -     do {
> > -             asm volatile (
> > -             "       ldex.w          %0, (%3)   \n"
> > -             "       movi            %2, 1      \n"
> > -             "       rotli           %1, %0, 16 \n"
> > -             "       cmpne           %1, %0     \n"
> > -             "       bt              1f         \n"
> > -             "       movi            %2, 0      \n"
> > -             "       add             %0, %0, %4 \n"
> > -             "       stex.w          %0, (%3)   \n"
> > -             "1:                                \n"
> > -             : "=&r" (res), "=&r" (tmp), "=&r" (contended)
> > -             : "r"(p), "r"(ticket_next)
> > -             : "cc");
> > -     } while (!res);
> > -
> > -     if (!contended)
> > -             smp_mb();
> > -
> > -     return !contended;
> > -}
> > -
> > -static inline void arch_spin_unlock(arch_spinlock_t *lock)
> > -{
> > -     smp_mb();
> > -     WRITE_ONCE(lock->tickets.owner, lock->tickets.owner + 1);
> > -}
> > -
> > -static inline int arch_spin_value_unlocked(arch_spinlock_t lock)
> > -{
> > -     return lock.tickets.owner == lock.tickets.next;
> > -}
> > -
> > -static inline int arch_spin_is_locked(arch_spinlock_t *lock)
> > -{
> > -     return !arch_spin_value_unlocked(READ_ONCE(*lock));
> > -}
> > -
> > -static inline int arch_spin_is_contended(arch_spinlock_t *lock)
> > -{
> > -     struct __raw_tickets tickets = READ_ONCE(lock->tickets);
> > -
> > -     return (tickets.next - tickets.owner) > 1;
> > -}
> > -#define arch_spin_is_contended       arch_spin_is_contended
> > -
> > +#include <asm/ticket-lock.h>
> >  #include <asm/qrwlock.h>
> >
> >  #endif /* __ASM_CSKY_SPINLOCK_H */
> > diff --git a/arch/csky/include/asm/spinlock_types.h b/arch/csky/include/asm/spinlock_types.h
> > index db87a12c3827..0bb7f6022a3b 100644
> > --- a/arch/csky/include/asm/spinlock_types.h
> > +++ b/arch/csky/include/asm/spinlock_types.h
> > @@ -3,25 +3,7 @@
> >  #ifndef __ASM_CSKY_SPINLOCK_TYPES_H
> >  #define __ASM_CSKY_SPINLOCK_TYPES_H
> >
> > -#ifndef __LINUX_SPINLOCK_TYPES_RAW_H
> > -# error "please don't include this file directly"
> > -#endif
> > -
> > -#define TICKET_NEXT  16
> > -
> > -typedef struct {
> > -     union {
> > -             u32 lock;
> > -             struct __raw_tickets {
> > -                     /* little endian */
> > -                     u16 owner;
> > -                     u16 next;
> > -             } tickets;
> > -     };
> > -} arch_spinlock_t;
> > -
> > -#define __ARCH_SPIN_LOCK_UNLOCKED    { { 0 } }
> > -
> > +#include <asm/ticket-lock-types.h>
> >  #include <asm-generic/qrwlock_types.h>
> >
> >  #endif /* __ASM_CSKY_SPINLOCK_TYPES_H */


-- 
Best Regards
 Guo Ren

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