[Mesa-dev] [PATCH v2 6/8] u_queue: add a futex-based implementation of fences
Marek Olšák
maraeo at gmail.com
Mon Nov 6 15:40:00 UTC 2017
Acked-by: Marek Olšák <marek.olsak at amd.com>
Marek
On Fri, Nov 3, 2017 at 9:09 PM, Nicolai Hähnle <nhaehnle at gmail.com> wrote:
> From: Nicolai Hähnle <nicolai.haehnle at amd.com>
>
> 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
> ---
> src/util/futex.h | 5 +++
> src/util/u_queue.c | 2 ++
> src/util/u_queue.h | 92 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 99 insertions(+)
>
> diff --git a/src/util/futex.h b/src/util/futex.h
> index 142c3b62f00..fa42cf4cf59 100644
> --- a/src/util/futex.h
> +++ b/src/util/futex.h
> @@ -36,18 +36,23 @@
> static inline long sys_futex(void *addr1, int op, int val1, struct timespec *timeout, void *addr2, int val3)
> {
> return syscall(SYS_futex, addr1, op, val1, timeout, addr2, val3);
> }
>
> static inline int futex_wake(uint32_t *addr)
> {
> return sys_futex(addr, FUTEX_WAKE, 1, NULL, NULL, 0);
> }
>
> +static inline int futex_wake_all(uint32_t *addr)
> +{
> + return sys_futex(addr, FUTEX_WAKE, INT_MAX, NULL, NULL, 0);
> +}
> +
> static inline int futex_wait(uint32_t *addr, int32_t value)
> {
> return sys_futex(addr, FUTEX_WAIT, value, NULL, NULL, 0);
> }
>
> #endif
>
> #endif /* UTIL_FUTEX_H */
> 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
> @@ -82,20 +82,21 @@ remove_from_atexit_list(struct util_queue *queue)
> break;
> }
> }
> mtx_unlock(&exit_mutex);
> }
>
> /****************************************************************************
> * util_queue_fence
> */
>
> +#ifdef UTIL_QUEUE_FENCE_STANDARD
> void
> util_queue_fence_signal(struct util_queue_fence *fence)
> {
> mtx_lock(&fence->mutex);
> fence->signalled = true;
> cnd_broadcast(&fence->cond);
> mtx_unlock(&fence->mutex);
> }
>
> void
> @@ -129,20 +130,21 @@ util_queue_fence_destroy(struct util_queue_fence *fence)
> * by thread A, thread B is allowed to destroy it. Since
> * util_queue_fence_is_signalled does not lock the fence mutex (for
> * performance reasons), we must do so here.
> */
> mtx_lock(&fence->mutex);
> mtx_unlock(&fence->mutex);
>
> cnd_destroy(&fence->cond);
> mtx_destroy(&fence->mutex);
> }
> +#endif
>
> /****************************************************************************
> * util_queue implementation
> */
>
> struct thread_input {
> struct util_queue *queue;
> int thread_index;
> };
>
> diff --git a/src/util/u_queue.h b/src/util/u_queue.h
> index a3e12260e30..be8e715899a 100644
> --- a/src/util/u_queue.h
> +++ b/src/util/u_queue.h
> @@ -28,30 +28,121 @@
> *
> * Jobs can be added from any thread. After that, the wait call can be used
> * to wait for completion of the job.
> */
>
> #ifndef U_QUEUE_H
> #define U_QUEUE_H
>
> #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
> extern "C" {
> #endif
>
> #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_all(&fence->val);
> +}
> +
> +/**
> + * 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.
> */
> struct util_queue_fence {
> mtx_t mutex;
> cnd_t cond;
> int signalled;
> };
>
> void util_queue_fence_init(struct util_queue_fence *fence);
> @@ -70,20 +161,21 @@ util_queue_fence_reset(struct util_queue_fence *fence)
> {
> assert(fence->signalled);
> fence->signalled = 0;
> }
>
> static inline bool
> 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);
>
> struct util_queue_job {
> void *job;
> struct util_queue_fence *fence;
> util_queue_execute_func execute;
> util_queue_execute_func cleanup;
> };
>
> --
> 2.11.0
>
> _______________________________________________
> mesa-dev mailing list
> mesa-dev at lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/mesa-dev
More information about the mesa-dev
mailing list