mirror of
git://git.yoctoproject.org/linux-yocto.git
synced 2025-10-23 07:23:12 +02:00

Add a separate ticket-lock.h to include multiple spinlock versions and select one at compile time or runtime. Reviewed-by: Leonardo Bras <leobras@redhat.com> Suggested-by: Arnd Bergmann <arnd@arndb.de> Link: https://lore.kernel.org/linux-riscv/CAK8P3a2rnz9mQqhN6-e0CGUUv9rntRELFdxt_weiD7FxH7fkfQ@mail.gmail.com/ Signed-off-by: Guo Ren <guoren@linux.alibaba.com> Signed-off-by: Guo Ren <guoren@kernel.org> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Andrew Jones <ajones@ventanamicro.com> Reviewed-by: Andrea Parri <parri.andrea@gmail.com> Link: https://lore.kernel.org/r/20241103145153.105097-11-alexghiti@rivosinc.com Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
104 lines
3.2 KiB
C
104 lines
3.2 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
|
|
|
|
/*
|
|
* 'Generic' ticket-lock implementation.
|
|
*
|
|
* It relies on atomic_fetch_add() having well defined forward progress
|
|
* guarantees under contention. If your architecture cannot provide this, stick
|
|
* to a test-and-set lock.
|
|
*
|
|
* It also relies on atomic_fetch_add() being safe vs smp_store_release() on a
|
|
* sub-word of the value. This is generally true for anything LL/SC although
|
|
* you'd be hard pressed to find anything useful in architecture specifications
|
|
* about this. If your architecture cannot do this you might be better off with
|
|
* a test-and-set.
|
|
*
|
|
* It further assumes atomic_*_release() + atomic_*_acquire() is RCpc and hence
|
|
* uses atomic_fetch_add() which is RCsc to create an RCsc hot path, along with
|
|
* a full fence after the spin to upgrade the otherwise-RCpc
|
|
* atomic_cond_read_acquire().
|
|
*
|
|
* The implementation uses smp_cond_load_acquire() to spin, so if the
|
|
* architecture has WFE like instructions to sleep instead of poll for word
|
|
* modifications be sure to implement that (see ARM64 for example).
|
|
*
|
|
*/
|
|
|
|
#ifndef __ASM_GENERIC_TICKET_SPINLOCK_H
|
|
#define __ASM_GENERIC_TICKET_SPINLOCK_H
|
|
|
|
#include <linux/atomic.h>
|
|
#include <asm-generic/spinlock_types.h>
|
|
|
|
static __always_inline void ticket_spin_lock(arch_spinlock_t *lock)
|
|
{
|
|
u32 val = atomic_fetch_add(1<<16, &lock->val);
|
|
u16 ticket = val >> 16;
|
|
|
|
if (ticket == (u16)val)
|
|
return;
|
|
|
|
/*
|
|
* atomic_cond_read_acquire() is RCpc, but rather than defining a
|
|
* custom cond_read_rcsc() here we just emit a full fence. We only
|
|
* need the prior reads before subsequent writes ordering from
|
|
* smb_mb(), but as atomic_cond_read_acquire() just emits reads and we
|
|
* have no outstanding writes due to the atomic_fetch_add() the extra
|
|
* orderings are free.
|
|
*/
|
|
atomic_cond_read_acquire(&lock->val, ticket == (u16)VAL);
|
|
smp_mb();
|
|
}
|
|
|
|
static __always_inline bool ticket_spin_trylock(arch_spinlock_t *lock)
|
|
{
|
|
u32 old = atomic_read(&lock->val);
|
|
|
|
if ((old >> 16) != (old & 0xffff))
|
|
return false;
|
|
|
|
return atomic_try_cmpxchg(&lock->val, &old, old + (1<<16)); /* SC, for RCsc */
|
|
}
|
|
|
|
static __always_inline void ticket_spin_unlock(arch_spinlock_t *lock)
|
|
{
|
|
u16 *ptr = (u16 *)lock + IS_ENABLED(CONFIG_CPU_BIG_ENDIAN);
|
|
u32 val = atomic_read(&lock->val);
|
|
|
|
smp_store_release(ptr, (u16)val + 1);
|
|
}
|
|
|
|
static __always_inline int ticket_spin_value_unlocked(arch_spinlock_t lock)
|
|
{
|
|
u32 val = lock.val.counter;
|
|
|
|
return ((val >> 16) == (val & 0xffff));
|
|
}
|
|
|
|
static __always_inline int ticket_spin_is_locked(arch_spinlock_t *lock)
|
|
{
|
|
arch_spinlock_t val = READ_ONCE(*lock);
|
|
|
|
return !ticket_spin_value_unlocked(val);
|
|
}
|
|
|
|
static __always_inline int ticket_spin_is_contended(arch_spinlock_t *lock)
|
|
{
|
|
u32 val = atomic_read(&lock->val);
|
|
|
|
return (s16)((val >> 16) - (val & 0xffff)) > 1;
|
|
}
|
|
|
|
/*
|
|
* Remapping spinlock architecture specific functions to the corresponding
|
|
* ticket spinlock functions.
|
|
*/
|
|
#define arch_spin_is_locked(l) ticket_spin_is_locked(l)
|
|
#define arch_spin_is_contended(l) ticket_spin_is_contended(l)
|
|
#define arch_spin_value_unlocked(l) ticket_spin_value_unlocked(l)
|
|
#define arch_spin_lock(l) ticket_spin_lock(l)
|
|
#define arch_spin_trylock(l) ticket_spin_trylock(l)
|
|
#define arch_spin_unlock(l) ticket_spin_unlock(l)
|
|
|
|
#endif /* __ASM_GENERIC_TICKET_SPINLOCK_H */
|