From: Guo Ren <guoren@kernel.org> To: Peter Zijlstra <peterz@infradead.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> Subject: Re: [PATCH] riscv: locks: introduce ticket-based spinlock implementation Date: Wed, 14 Apr 2021 10:26:57 +0800 [thread overview] Message-ID: <CAJF2gTQaF8wBCp-L6vgJPcu6EnFRWmh_qZMX2PiEfj0Z70-Ykg@mail.gmail.com> (raw) In-Reply-To: <YHVTgfCpxpINc8sM@hirez.programming.kicks-ass.net> Thx Peter, On Tue, Apr 13, 2021 at 4:17 PM Peter Zijlstra <peterz@infradead.org> wrote: > > On Tue, Apr 13, 2021 at 10:03:01AM +0200, Peter Zijlstra wrote: > > > For ticket locks you really only needs atomic_fetch_add() and > > smp_store_release() and an architectural guarantees that the > > atomic_fetch_add() has fwd progress under contention and that a sub-word > > store (through smp_store_release()) will fail the SC. > > > > Then you can do something like: > > > > void lock(atomic_t *lock) > > { > > u32 val = atomic_fetch_add(1<<16, lock); /* SC, gives us RCsc */ > > u16 ticket = val >> 16; > > > > for (;;) { > > if (ticket == (u16)val) > > break; > > cpu_relax(); > > val = atomic_read_acquire(lock); > > } Should it be? for (;;) { if (ticket == (u16)val) { __atomic_acquire_fence(); break; } > > A possibly better might be: > > if (ticket == (u16)val) > return; Should it be? if (ticket == (u16)val) { __atomic_acquire_fence(); return; } > > atomic_cond_read_acquire(lock, ticket == (u16)VAL); > > Since that allows architectures to use WFE like constructs. > > > } > > > > void unlock(atomic_t *lock) > > { > > u16 *ptr = (u16 *)lock + (!!__BIG_ENDIAN__); > > u32 val = atomic_read(lock); > > > > smp_store_release(ptr, (u16)val + 1); > > } > > > > That's _almost_ as simple as a test-and-set :-) It isn't quite optimal > > on x86 for not being allowed to use a memop on unlock, since its being > > forced into a load-store because of all the volatile, but whatever. -- Best Regards Guo Ren ML: https://lore.kernel.org/linux-csky/
WARNING: multiple messages have this Message-ID (diff)
From: Guo Ren <guoren@kernel.org> To: Peter Zijlstra <peterz@infradead.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> Subject: Re: [PATCH] riscv: locks: introduce ticket-based spinlock implementation Date: Wed, 14 Apr 2021 10:26:57 +0800 [thread overview] Message-ID: <CAJF2gTQaF8wBCp-L6vgJPcu6EnFRWmh_qZMX2PiEfj0Z70-Ykg@mail.gmail.com> (raw) In-Reply-To: <YHVTgfCpxpINc8sM@hirez.programming.kicks-ass.net> Thx Peter, On Tue, Apr 13, 2021 at 4:17 PM Peter Zijlstra <peterz@infradead.org> wrote: > > On Tue, Apr 13, 2021 at 10:03:01AM +0200, Peter Zijlstra wrote: > > > For ticket locks you really only needs atomic_fetch_add() and > > smp_store_release() and an architectural guarantees that the > > atomic_fetch_add() has fwd progress under contention and that a sub-word > > store (through smp_store_release()) will fail the SC. > > > > Then you can do something like: > > > > void lock(atomic_t *lock) > > { > > u32 val = atomic_fetch_add(1<<16, lock); /* SC, gives us RCsc */ > > u16 ticket = val >> 16; > > > > for (;;) { > > if (ticket == (u16)val) > > break; > > cpu_relax(); > > val = atomic_read_acquire(lock); > > } Should it be? for (;;) { if (ticket == (u16)val) { __atomic_acquire_fence(); break; } > > A possibly better might be: > > if (ticket == (u16)val) > return; Should it be? if (ticket == (u16)val) { __atomic_acquire_fence(); return; } > > atomic_cond_read_acquire(lock, ticket == (u16)VAL); > > Since that allows architectures to use WFE like constructs. > > > } > > > > void unlock(atomic_t *lock) > > { > > u16 *ptr = (u16 *)lock + (!!__BIG_ENDIAN__); > > u32 val = atomic_read(lock); > > > > smp_store_release(ptr, (u16)val + 1); > > } > > > > That's _almost_ as simple as a test-and-set :-) It isn't quite optimal > > on x86 for not being allowed to use a memop on unlock, since its being > > forced into a load-store because of all the volatile, but whatever. -- Best Regards Guo Ren ML: https://lore.kernel.org/linux-csky/ _______________________________________________ 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 2:27 UTC|newest] Thread overview: 98+ 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 [this message] 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 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 2021-09-19 16:53 guoren 2021-09-19 16:53 ` guoren 2021-09-25 14:47 ` Guo Ren 2021-09-25 14:47 ` Guo Ren 2021-10-21 13:13 ` Peter Zijlstra 2021-10-21 13:13 ` Peter Zijlstra
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