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Date:   Tue, 22 Mar 2022 10:48:32 -0700 (PDT)
Subject:     Re: [PATCH] csky: Move to generic ticket-spinlock
In-Reply-To: <CAJF2gTShUjTQ=7g3uW8JmPzkZSG0fWKK7fXgAsERSUfrCgzA0w@mail.gmail.com>
CC:     linux-csky@vger.kernel.org, linux-arch@vger.kernel.org,
        linux-kernel@vger.kernel.org, guoren@linux.alibaba.com
From:   Palmer Dabbelt <palmer@rivosinc.com>
To:     guoren@kernel.org
Message-ID: <mhng-382a4c87-1d59-43ba-b567-06c6eb94843e@palmer-ri-x1c9>
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On Fri, 18 Mar 2022 21:01:49 PDT (-0700), guoren@kernel.org wrote:
> 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

Thanks, I'll include the csky stuff next time I re-spin this.

Looks like there's been some other comments from folks that didn't make 
your v2, most notably the SOB lines which makes this a bit funny.  I'm 
also not sure I like merging the two RISC-V patches together, as they'd 
be nice to be able to test on their own.

I'll go poke around with this some once I'm a bit father into the merge 
window.  I think we can both keep Arnd's generic header idea and let 
folks mix/match spin/rw lock flavors, which might also help with some of 
the other ports.


>
>>
>> > ---
>> >  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 */