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-rw-r--r--arch/tile/lib/spinlock_32.c161
1 files changed, 96 insertions, 65 deletions
diff --git a/arch/tile/lib/spinlock_32.c b/arch/tile/lib/spinlock_32.c
index 5cd1c40..cb0999f 100644
--- a/arch/tile/lib/spinlock_32.c
+++ b/arch/tile/lib/spinlock_32.c
@@ -15,6 +15,7 @@
#include <linux/spinlock.h>
#include <linux/module.h>
#include <asm/processor.h>
+#include <arch/spr_def.h>
#include "spinlock_common.h"
@@ -91,75 +92,75 @@ EXPORT_SYMBOL(arch_spin_unlock_wait);
#define RD_COUNT_MASK ((1 << RD_COUNT_WIDTH) - 1)
-/* Lock the word, spinning until there are no tns-ers. */
-static inline u32 get_rwlock(arch_rwlock_t *rwlock)
-{
- u32 iterations = 0;
- for (;;) {
- u32 val = __insn_tns((int *)&rwlock->lock);
- if (unlikely(val & 1)) {
- delay_backoff(iterations++);
- continue;
- }
- return val;
- }
-}
-
-int arch_read_trylock_slow(arch_rwlock_t *rwlock)
-{
- u32 val = get_rwlock(rwlock);
- int locked = (val << RD_COUNT_WIDTH) == 0;
- rwlock->lock = val + (locked << RD_COUNT_SHIFT);
- return locked;
-}
-EXPORT_SYMBOL(arch_read_trylock_slow);
-
-void arch_read_unlock_slow(arch_rwlock_t *rwlock)
-{
- u32 val = get_rwlock(rwlock);
- rwlock->lock = val - (1 << RD_COUNT_SHIFT);
-}
-EXPORT_SYMBOL(arch_read_unlock_slow);
-
-void arch_write_unlock_slow(arch_rwlock_t *rwlock, u32 val)
+/*
+ * We can get the read lock if everything but the reader bits (which
+ * are in the high part of the word) is zero, i.e. no active or
+ * waiting writers, no tns.
+ *
+ * We guard the tns/store-back with an interrupt critical section to
+ * preserve the semantic that the same read lock can be acquired in an
+ * interrupt context.
+ */
+inline int arch_read_trylock(arch_rwlock_t *rwlock)
{
- u32 eq, mask = 1 << WR_CURR_SHIFT;
- while (unlikely(val & 1)) {
- /* Limited backoff since we are the highest-priority task. */
- relax(4);
- val = __insn_tns((int *)&rwlock->lock);
+ u32 val;
+ __insn_mtspr(SPR_INTERRUPT_CRITICAL_SECTION, 1);
+ val = __insn_tns((int *)&rwlock->lock);
+ if (likely((val << _RD_COUNT_WIDTH) == 0)) {
+ val += 1 << RD_COUNT_SHIFT;
+ rwlock->lock = val;
+ __insn_mtspr(SPR_INTERRUPT_CRITICAL_SECTION, 0);
+ BUG_ON(val == 0); /* we don't expect wraparound */
+ return 1;
}
- val = __insn_addb(val, mask);
- eq = __insn_seqb(val, val << (WR_CURR_SHIFT - WR_NEXT_SHIFT));
- val = __insn_mz(eq & mask, val);
- rwlock->lock = val;
+ if ((val & 1) == 0)
+ rwlock->lock = val;
+ __insn_mtspr(SPR_INTERRUPT_CRITICAL_SECTION, 0);
+ return 0;
}
-EXPORT_SYMBOL(arch_write_unlock_slow);
+EXPORT_SYMBOL(arch_read_trylock);
/*
- * We spin until everything but the reader bits (which are in the high
- * part of the word) are zero, i.e. no active or waiting writers, no tns.
- *
+ * Spin doing arch_read_trylock() until we acquire the lock.
* ISSUE: This approach can permanently starve readers. A reader who sees
* a writer could instead take a ticket lock (just like a writer would),
* and atomically enter read mode (with 1 reader) when it gets the ticket.
- * This way both readers and writers will always make forward progress
+ * This way both readers and writers would always make forward progress
* in a finite time.
*/
-void arch_read_lock_slow(arch_rwlock_t *rwlock, u32 val)
+void arch_read_lock(arch_rwlock_t *rwlock)
{
u32 iterations = 0;
- do {
- if (!(val & 1))
- rwlock->lock = val;
+ while (unlikely(!arch_read_trylock(rwlock)))
delay_backoff(iterations++);
+}
+EXPORT_SYMBOL(arch_read_lock);
+
+void arch_read_unlock(arch_rwlock_t *rwlock)
+{
+ u32 val, iterations = 0;
+
+ mb(); /* guarantee anything modified under the lock is visible */
+ for (;;) {
+ __insn_mtspr(SPR_INTERRUPT_CRITICAL_SECTION, 1);
val = __insn_tns((int *)&rwlock->lock);
- } while ((val << RD_COUNT_WIDTH) != 0);
- rwlock->lock = val + (1 << RD_COUNT_SHIFT);
+ if (likely(val & 1) == 0) {
+ rwlock->lock = val - (1 << _RD_COUNT_SHIFT);
+ __insn_mtspr(SPR_INTERRUPT_CRITICAL_SECTION, 0);
+ break;
+ }
+ __insn_mtspr(SPR_INTERRUPT_CRITICAL_SECTION, 0);
+ delay_backoff(iterations++);
+ }
}
-EXPORT_SYMBOL(arch_read_lock_slow);
+EXPORT_SYMBOL(arch_read_unlock);
-void arch_write_lock_slow(arch_rwlock_t *rwlock, u32 val)
+/*
+ * We don't need an interrupt critical section here (unlike for
+ * arch_read_lock) since we should never use a bare write lock where
+ * it could be interrupted by code that could try to re-acquire it.
+ */
+void arch_write_lock(arch_rwlock_t *rwlock)
{
/*
* The trailing underscore on this variable (and curr_ below)
@@ -168,6 +169,12 @@ void arch_write_lock_slow(arch_rwlock_t *rwlock, u32 val)
*/
u32 my_ticket_;
u32 iterations = 0;
+ u32 val = __insn_tns((int *)&rwlock->lock);
+
+ if (likely(val == 0)) {
+ rwlock->lock = 1 << _WR_NEXT_SHIFT;
+ return;
+ }
/*
* Wait until there are no readers, then bump up the next
@@ -206,23 +213,47 @@ void arch_write_lock_slow(arch_rwlock_t *rwlock, u32 val)
relax(4);
}
}
-EXPORT_SYMBOL(arch_write_lock_slow);
+EXPORT_SYMBOL(arch_write_lock);
-int __tns_atomic_acquire(atomic_t *lock)
+int arch_write_trylock(arch_rwlock_t *rwlock)
{
- int ret;
- u32 iterations = 0;
+ u32 val = __insn_tns((int *)&rwlock->lock);
- BUG_ON(__insn_mfspr(SPR_INTERRUPT_CRITICAL_SECTION));
- __insn_mtspr(SPR_INTERRUPT_CRITICAL_SECTION, 1);
+ /*
+ * If a tns is in progress, or there's a waiting or active locker,
+ * or active readers, we can't take the lock, so give up.
+ */
+ if (unlikely(val != 0)) {
+ if (!(val & 1))
+ rwlock->lock = val;
+ return 0;
+ }
- while ((ret = __insn_tns((void *)&lock->counter)) == 1)
- delay_backoff(iterations++);
- return ret;
+ /* Set the "next" field to mark it locked. */
+ rwlock->lock = 1 << _WR_NEXT_SHIFT;
+ return 1;
}
+EXPORT_SYMBOL(arch_write_trylock);
-void __tns_atomic_release(atomic_t *p, int v)
+void arch_write_unlock(arch_rwlock_t *rwlock)
{
- p->counter = v;
- __insn_mtspr(SPR_INTERRUPT_CRITICAL_SECTION, 0);
+ u32 val, eq, mask;
+
+ mb(); /* guarantee anything modified under the lock is visible */
+ val = __insn_tns((int *)&rwlock->lock);
+ if (likely(val == (1 << _WR_NEXT_SHIFT))) {
+ rwlock->lock = 0;
+ return;
+ }
+ while (unlikely(val & 1)) {
+ /* Limited backoff since we are the highest-priority task. */
+ relax(4);
+ val = __insn_tns((int *)&rwlock->lock);
+ }
+ mask = 1 << WR_CURR_SHIFT;
+ val = __insn_addb(val, mask);
+ eq = __insn_seqb(val, val << (WR_CURR_SHIFT - WR_NEXT_SHIFT));
+ val = __insn_mz(eq & mask, val);
+ rwlock->lock = val;
}
+EXPORT_SYMBOL(arch_write_unlock);
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