From d1ff0826370cb1cfbcf741c8eb35caf1fddd7d52 Mon Sep 17 00:00:00 2001 From: =?utf8?q?Nicolai=20H=C3=A4hnle?= Date: Sun, 22 Oct 2017 17:38:31 +0200 Subject: [PATCH] u_queue: add a futex-based implementation of fences MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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 --- src/util/u_queue.c | 2 + src/util/u_queue.h | 92 ++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 94 insertions(+) diff --git a/src/util/u_queue.c b/src/util/u_queue.c index 2272006042f..8293ec661b0 100644 --- a/src/util/u_queue.c +++ b/src/util/u_queue.c @@ -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 diff --git a/src/util/u_queue.h b/src/util/u_queue.h index a3e12260e30..dfe21532817 100644 --- a/src/util/u_queue.h +++ b/src/util/u_queue.h @@ -35,7 +35,10 @@ #include +#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); -- 2.30.2