From: Peter Zijlstra <peterz@infradead.org> To: Guo Ren <guoren@kernel.org> Cc: "Christoph Müllner" <christophm30@gmail.com>, "Palmer Dabbelt" <palmer@dabbelt.com>, "Anup Patel" <anup@brainfault.org>, linux-riscv <linux-riscv@lists.infradead.org>, "Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>, "Guo Ren" <guoren@linux.alibaba.com>, "Catalin Marinas" <catalin.marinas@arm.com>, "Will Deacon" <will.deacon@arm.com>, "Arnd Bergmann" <arnd@arndb.de>, "Jonas Bonn" <jonas@southpole.se>, "Stefan Kristiansson" <stefan.kristiansson@saunalahti.fi>, "Stafford Horne" <shorne@gmail.com> Subject: Re: [RFC][PATCH] locking: Generic ticket-lock Date: Wed, 14 Apr 2021 14:55:57 +0200 [thread overview] Message-ID: <YHbmXXvuG442ZDfN@hirez.programming.kicks-ass.net> (raw) In-Reply-To: <CAJF2gTRsQQ=RunxK6R9MfK70dULt=RJOXXGCOT9oDPEsBgvKtQ@mail.gmail.com> On Wed, Apr 14, 2021 at 08:39:33PM +0800, Guo Ren wrote: > I've tested it on csky SMP*4 hw (860) & riscv SMP*4 hw (c910) and it's okay. W00t :-) > Hope you can keep > typedef struct { > union { > atomic_t lock; > struct __raw_tickets { > #ifdef __BIG_ENDIAN > u16 next; > u16 owner; > #else > u16 owner; > u16 next; > #endif > } tickets; > }; > } arch_spinlock_t; > > Using owner & next is much more readable. That almost doubles the line-count of the thing ;-) > > + * It further assumes atomic_*_release() + atomic_*_acquire() is RCpc and hence > > + * uses atomic_fetch_add() which is SC to create an RCsc lock. This ^^^ then vvv > > +static __always_inline void ticket_lock(arch_spinlock_t *lock) > > +{ > > + u32 val = atomic_fetch_add(1<<16, lock); /* SC, gives us RCsc */ > atomic_fetch_add_acquire ? Then we must rely on the arch to implement RCsc atomics. And I for one can never tell wth Risc-V actually does. > > +static __always_inline int ticket_is_locked(arch_spinlock_t *lock) > > +{ > > + u32 val = atomic_read(lock); > > + > > + return ((val >> 16) != (val & 0xffff)); > I perfer: > return !arch_spin_value_unlocked(READ_ONCE(*lock)); > > +} > > +} > > + > > +static __always_inline int ticket_value_unlocked(arch_spinlock_t lock) > > +{ > > + return !ticket_is_locked(&lock); > Are you sure to let ticket_is_locked->atomic_read(lock) again, the > lock has contained all information? > > return lock.tickets.owner == lock.tickets.next; Yeah, I wrote then the wrong way around. Couldn't be bothered to go back when I figured it out. > > + > > +static __always_inline int ticket_is_contended(arch_spinlock_t *lock) > > +{ > > + u32 val = atomic_read(lock); > > + > > + return (s16)((val >> 16) - (val & 0xffff)) > 1; > How big-endian ? How not? Endian-ness only matters when you go poke at sub-words, which the above does not. Only ticket_unlock() does and cares about that.
WARNING: multiple messages have this Message-ID (diff)
From: Peter Zijlstra <peterz@infradead.org> To: Guo Ren <guoren@kernel.org> Cc: "Christoph Müllner" <christophm30@gmail.com>, "Palmer Dabbelt" <palmer@dabbelt.com>, "Anup Patel" <anup@brainfault.org>, linux-riscv <linux-riscv@lists.infradead.org>, "Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>, "Guo Ren" <guoren@linux.alibaba.com>, "Catalin Marinas" <catalin.marinas@arm.com>, "Will Deacon" <will.deacon@arm.com>, "Arnd Bergmann" <arnd@arndb.de>, "Jonas Bonn" <jonas@southpole.se>, "Stefan Kristiansson" <stefan.kristiansson@saunalahti.fi>, "Stafford Horne" <shorne@gmail.com> Subject: Re: [RFC][PATCH] locking: Generic ticket-lock Date: Wed, 14 Apr 2021 14:55:57 +0200 [thread overview] Message-ID: <YHbmXXvuG442ZDfN@hirez.programming.kicks-ass.net> (raw) In-Reply-To: <CAJF2gTRsQQ=RunxK6R9MfK70dULt=RJOXXGCOT9oDPEsBgvKtQ@mail.gmail.com> On Wed, Apr 14, 2021 at 08:39:33PM +0800, Guo Ren wrote: > I've tested it on csky SMP*4 hw (860) & riscv SMP*4 hw (c910) and it's okay. W00t :-) > Hope you can keep > typedef struct { > union { > atomic_t lock; > struct __raw_tickets { > #ifdef __BIG_ENDIAN > u16 next; > u16 owner; > #else > u16 owner; > u16 next; > #endif > } tickets; > }; > } arch_spinlock_t; > > Using owner & next is much more readable. That almost doubles the line-count of the thing ;-) > > + * It further assumes atomic_*_release() + atomic_*_acquire() is RCpc and hence > > + * uses atomic_fetch_add() which is SC to create an RCsc lock. This ^^^ then vvv > > +static __always_inline void ticket_lock(arch_spinlock_t *lock) > > +{ > > + u32 val = atomic_fetch_add(1<<16, lock); /* SC, gives us RCsc */ > atomic_fetch_add_acquire ? Then we must rely on the arch to implement RCsc atomics. And I for one can never tell wth Risc-V actually does. > > +static __always_inline int ticket_is_locked(arch_spinlock_t *lock) > > +{ > > + u32 val = atomic_read(lock); > > + > > + return ((val >> 16) != (val & 0xffff)); > I perfer: > return !arch_spin_value_unlocked(READ_ONCE(*lock)); > > +} > > +} > > + > > +static __always_inline int ticket_value_unlocked(arch_spinlock_t lock) > > +{ > > + return !ticket_is_locked(&lock); > Are you sure to let ticket_is_locked->atomic_read(lock) again, the > lock has contained all information? > > return lock.tickets.owner == lock.tickets.next; Yeah, I wrote then the wrong way around. Couldn't be bothered to go back when I figured it out. > > + > > +static __always_inline int ticket_is_contended(arch_spinlock_t *lock) > > +{ > > + u32 val = atomic_read(lock); > > + > > + return (s16)((val >> 16) - (val & 0xffff)) > 1; > How big-endian ? How not? Endian-ness only matters when you go poke at sub-words, which the above does not. Only ticket_unlock() does and cares about that. _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv
next prev parent reply other threads:[~2021-04-14 12:57 UTC|newest] Thread overview: 92+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-03-24 10:14 [PATCH] riscv: locks: introduce ticket-based spinlock implementation guoren 2021-03-24 10:14 ` guoren 2021-03-24 11:09 ` Peter Zijlstra 2021-03-24 11:09 ` Peter Zijlstra 2021-03-24 12:10 ` Guo Ren 2021-03-24 12:10 ` Guo Ren [not found] ` <CAM4kBBK7_s9U2vJbq68yC8WdDEfPQTaCOvn1xds3Si5B-Wpw+A@mail.gmail.com> 2021-03-24 12:23 ` Peter Zijlstra 2021-03-24 12:23 ` Peter Zijlstra 2021-03-24 12:24 ` Guo Ren 2021-03-24 12:24 ` Guo Ren 2021-03-24 12:31 ` Peter Zijlstra 2021-03-24 12:31 ` Peter Zijlstra 2021-03-24 12:28 ` Anup Patel 2021-03-24 12:28 ` Anup Patel 2021-03-24 12:37 ` Peter Zijlstra 2021-03-24 12:37 ` Peter Zijlstra 2021-03-24 12:53 ` Anup Patel 2021-03-24 12:53 ` Anup Patel 2021-04-11 21:11 ` Palmer Dabbelt 2021-04-11 21:11 ` Palmer Dabbelt 2021-04-12 13:32 ` Christoph Müllner 2021-04-12 13:32 ` Christoph Müllner 2021-04-12 14:51 ` Peter Zijlstra 2021-04-12 14:51 ` Peter Zijlstra 2021-04-12 21:21 ` Christoph Müllner 2021-04-12 21:21 ` Christoph Müllner 2021-04-12 17:33 ` Palmer Dabbelt 2021-04-12 17:33 ` Palmer Dabbelt 2021-04-12 21:54 ` Christoph Müllner 2021-04-12 21:54 ` Christoph Müllner 2021-04-13 8:03 ` Peter Zijlstra 2021-04-13 8:03 ` Peter Zijlstra 2021-04-13 8:17 ` Peter Zijlstra 2021-04-13 8:17 ` Peter Zijlstra 2021-04-14 2:26 ` Guo Ren 2021-04-14 2:26 ` Guo Ren 2021-04-14 7:08 ` Peter Zijlstra 2021-04-14 7:08 ` Peter Zijlstra 2021-04-14 9:05 ` Peter Zijlstra 2021-04-14 9:05 ` Peter Zijlstra 2021-04-14 10:16 ` [RFC][PATCH] locking: Generic ticket-lock Peter Zijlstra 2021-04-14 10:16 ` Peter Zijlstra 2021-04-14 12:39 ` Guo Ren 2021-04-14 12:39 ` Guo Ren 2021-04-14 12:55 ` Peter Zijlstra [this message] 2021-04-14 12:55 ` Peter Zijlstra 2021-04-14 13:08 ` Peter Zijlstra 2021-04-14 13:08 ` Peter Zijlstra 2021-04-14 15:59 ` David Laight 2021-04-14 15:59 ` David Laight 2021-04-14 12:45 ` Peter Zijlstra 2021-04-14 12:45 ` Peter Zijlstra 2021-04-14 21:02 ` Stafford Horne 2021-04-14 21:02 ` Stafford Horne 2021-04-14 20:47 ` Stafford Horne 2021-04-14 20:47 ` Stafford Horne 2021-04-15 8:09 ` Peter Zijlstra 2021-04-15 8:09 ` Peter Zijlstra 2021-04-15 9:02 ` Catalin Marinas 2021-04-15 9:02 ` Catalin Marinas 2021-04-15 9:22 ` Will Deacon 2021-04-15 9:22 ` Will Deacon 2021-04-15 9:24 ` Peter Zijlstra 2021-04-15 9:24 ` Peter Zijlstra 2021-04-19 17:35 ` Will Deacon 2021-04-19 17:35 ` Will Deacon 2021-04-23 6:44 ` Palmer Dabbelt 2021-04-23 6:44 ` Palmer Dabbelt 2021-04-13 9:22 ` [PATCH] riscv: locks: introduce ticket-based spinlock implementation Christoph Müllner 2021-04-13 9:22 ` Christoph Müllner 2021-04-13 9:30 ` Catalin Marinas 2021-04-13 9:30 ` Catalin Marinas 2021-04-13 9:55 ` Christoph Müllner 2021-04-13 9:55 ` Christoph Müllner 2021-04-14 0:23 ` Guo Ren 2021-04-14 0:23 ` Guo Ren 2021-04-14 9:17 ` Catalin Marinas 2021-04-14 9:17 ` Catalin Marinas 2021-04-13 9:35 ` Peter Zijlstra 2021-04-13 9:35 ` Peter Zijlstra 2021-04-13 10:25 ` Christoph Müllner 2021-04-13 10:25 ` Christoph Müllner 2021-04-13 10:45 ` Catalin Marinas 2021-04-13 10:45 ` Catalin Marinas 2021-04-13 10:54 ` David Laight 2021-04-13 10:54 ` David Laight 2021-04-14 5:54 ` Guo Ren 2021-04-14 5:54 ` Guo Ren 2021-04-13 11:04 ` Christoph Müllner 2021-04-13 11:04 ` Christoph Müllner 2021-04-13 13:19 ` Guo Ren 2021-04-13 13:19 ` Guo Ren
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