Re: [PATCH] csky: Move to generic ticket-spinlock

From: Palmer Dabbelt
Date: Tue Mar 22 2022 - 13:48:41 EST

On Fri, 18 Mar 2022 21:01:49 PDT (-0700), guoren@xxxxxxxxxx wrote:
Hi Palmer,

On Sat, Mar 19, 2022 at 6:48 AM Palmer Dabbelt <palmer@xxxxxxxxxxxx> wrote:

On Fri, 18 Mar 2022 01:34:21 PDT (-0700), guoren@xxxxxxxxxx wrote:
> From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
>
> 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@xxxxxxxxxxxxxxxxx>
> Cc: Palmer Dabbelt <palmer@xxxxxxxxxxxx>

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@xxxxxxxxxx/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 */