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u_queue: add a futex-based implementation of fences

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Fences are now 4 bytes instead of 96 bytes (on my 64-bit system).

Signaling a fence is a single atomic operation in the fast case plus a
syscall in the slow case.

Testing if a fence is signaled is the same as before (a simple comparison),
but waiting on a fence is now no more expensive than just testing it in
the fast (already signaled) case.

v2:
- style fixes
- use p_atomic_xxx macros with the right barriers

Acked-by: Marek Olšák <marek.olsak@amd.com>
This commit is contained in:
Nicolai Hähnle 2017-10-22 17:38:31 +02:00
parent 574c59d4f9
commit d1ff082637
2 changed files with 94 additions and 0 deletions
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2
src/util/u_queue.c
View file

@ -89,6 +89,7 @@ remove_from_atexit_list(struct util_queue *queue)
* util_queue_fence
*/
#ifdef UTIL_QUEUE_FENCE_STANDARD
void
util_queue_fence_signal(struct util_queue_fence *fence)
{
@ -136,6 +137,7 @@ util_queue_fence_destroy(struct util_queue_fence *fence)
cnd_destroy(&fence->cond);
mtx_destroy(&fence->mutex);
}
#endif
/****************************************************************************
* util_queue implementation

92
src/util/u_queue.h
View file

@ -35,7 +35,10 @@
#include <string.h>
#include "util/futex.h"
#include "util/list.h"
#include "util/macros.h"
#include "util/u_atomic.h"
#include "util/u_thread.h"
#ifdef __cplusplus
@ -45,6 +48,94 @@ extern "C" {
#define UTIL_QUEUE_INIT_USE_MINIMUM_PRIORITY (1 << 0)
#define UTIL_QUEUE_INIT_RESIZE_IF_FULL (1 << 1)
#if defined(__GNUC__) && defined(HAVE_FUTEX)
#define UTIL_QUEUE_FENCE_FUTEX
#else
#define UTIL_QUEUE_FENCE_STANDARD
#endif
#ifdef UTIL_QUEUE_FENCE_FUTEX
/* Job completion fence.
* Put this into your job structure.
*/
struct util_queue_fence {
/* The fence can be in one of three states:
* 0 - signaled
* 1 - unsignaled
* 2 - unsignaled, may have waiters
*/
uint32_t val;
};
static inline void
util_queue_fence_init(struct util_queue_fence *fence)
{
fence->val = 0;
}
static inline void
util_queue_fence_destroy(struct util_queue_fence *fence)
{
assert(fence->val == 0);
/* no-op */
}
static inline void
util_queue_fence_wait(struct util_queue_fence *fence)
{
uint32_t v = fence->val;
if (likely(v == 0))
return;
do {
if (v != 2) {
v = p_atomic_cmpxchg(&fence->val, 1, 2);
if (v == 0)
return;
}
futex_wait(&fence->val, 2);
v = fence->val;
} while(v != 0);
}
static inline void
util_queue_fence_signal(struct util_queue_fence *fence)
{
uint32_t val = p_atomic_xchg(&fence->val, 0);
assert(val != 0);
if (val == 2)
futex_wake(&fence->val, INT_MAX);
}
/**
* Move \p fence back into unsignalled state.
*
* \warning The caller must ensure that no other thread may currently be
* waiting (or about to wait) on the fence.
*/
static inline void
util_queue_fence_reset(struct util_queue_fence *fence)
{
#ifdef NDEBUG
fence->val = 1;
#else
uint32_t v = p_atomic_xchg(&fence->val, 1);
assert(v == 0);
#endif
}
static inline bool
util_queue_fence_is_signalled(struct util_queue_fence *fence)
{
return fence->val == 0;
}
#endif
#ifdef UTIL_QUEUE_FENCE_STANDARD
/* Job completion fence.
* Put this into your job structure.
*/
@ -77,6 +168,7 @@ util_queue_fence_is_signalled(struct util_queue_fence *fence)
{
return fence->signalled != 0;
}
#endif
typedef void (*util_queue_execute_func)(void *job, int thread_index);