On Wed, 07 Jun 2017 06:17:27 PDT (-0700), [email protected] wrote: > On Tue, Jun 06, 2017 at 04:00:03PM -0700, Palmer Dabbelt wrote: >> diff --git a/arch/riscv/include/asm/spinlock.h >> b/arch/riscv/include/asm/spinlock.h >> new file mode 100644 >> index 000000000000..9736f5714e54 >> --- /dev/null >> +++ b/arch/riscv/include/asm/spinlock.h >> @@ -0,0 +1,155 @@ >> +/* >> + * Copyright (C) 2015 Regents of the University of California >> + * >> + * This program is free software; you can redistribute it and/or >> + * modify it under the terms of the GNU General Public License >> + * as published by the Free Software Foundation, version 2. >> + * >> + * This program is distributed in the hope that it will be useful, >> + * but WITHOUT ANY WARRANTY; without even the implied warranty of >> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the >> + * GNU General Public License for more details. >> + */ >> + >> +#ifndef _ASM_RISCV_SPINLOCK_H >> +#define _ASM_RISCV_SPINLOCK_H >> + >> +#include <linux/kernel.h> >> +#include <asm/current.h> >> + >> +/* >> + * Simple spin lock operations. These provide no fairness guarantees. >> + */ > > Any reason to use a test-and-set spinlock at all?
Just simplicity. I looked at the MIPS ticket lock and I think we can implement that while still maintaining the forward progress constraints on our LR/SC sequences. I added a FIXME about it, which I'll try to get around to https://github.com/riscv/riscv-linux/commit/a75d28c849e695639b7909ffa88ce571abfb0c76 but I'm going to try and get a v3 patch set out first. >> + >> +#define arch_spin_lock_flags(lock, flags) arch_spin_lock(lock) >> +#define arch_spin_is_locked(x) ((x)->lock != 0) >> +#define arch_spin_unlock_wait(x) \ >> + do { cpu_relax(); } while ((x)->lock) > > Hehe, yeah, no ;-) There are ordering constraints on that. OK. I copied the ordering guarntees from MIPS here https://github.com/riscv/riscv-linux/commit/7d16920452c6bd14c847aade2d51c56d2a1ae457 >> + >> +static inline void arch_spin_unlock(arch_spinlock_t *lock) >> +{ >> + __asm__ __volatile__ ( >> + "amoswap.w.rl x0, x0, %0" >> + : "=A" (lock->lock) >> + :: "memory"); >> +} >> + >> +static inline int arch_spin_trylock(arch_spinlock_t *lock) >> +{ >> + int tmp = 1, busy; >> + >> + __asm__ __volatile__ ( >> + "amoswap.w.aq %0, %2, %1" >> + : "=r" (busy), "+A" (lock->lock) >> + : "r" (tmp) >> + : "memory"); >> + >> + return !busy; >> +} >> + >> +static inline void arch_spin_lock(arch_spinlock_t *lock) >> +{ >> + while (1) { >> + if (arch_spin_is_locked(lock)) >> + continue; >> + >> + if (arch_spin_trylock(lock)) >> + break; >> + } >> +} Thanks for all the comments!
