[RESEND PATCH 2/5] drm: Add Reusable task barrier.
Ma, Le
Le.Ma at amd.com
Thu Dec 12 04:04:34 UTC 2019
[AMD Official Use Only - Internal Distribution Only]
-----Original Message-----
From: Andrey Grodzovsky <andrey.grodzovsky at amd.com>
Sent: Thursday, December 12, 2019 4:39 AM
To: dri-devel at lists.freedesktop.org; amd-gfx at lists.freedesktop.org
Cc: Deucher, Alexander <Alexander.Deucher at amd.com>; Ma, Le <Le.Ma at amd.com>; Zhang, Hawking <Hawking.Zhang at amd.com>; Quan, Evan <Evan.Quan at amd.com>; Grodzovsky, Andrey <Andrey.Grodzovsky at amd.com>
Subject: [RESEND PATCH 2/5] drm: Add Reusable task barrier.
It is used to synchronize N threads at a rendevouz point before execution of critical code that has to be started by all the threads at approximatly the same time.
Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky at amd.com<mailto:andrey.grodzovsky at amd.com>>
---
include/drm/task_barrier.h | 106 +++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 106 insertions(+)
create mode 100644 include/drm/task_barrier.h
diff --git a/include/drm/task_barrier.h b/include/drm/task_barrier.h new file mode 100644 index 0000000..81fb0f7
--- /dev/null
+++ b/include/drm/task_barrier.h
@@ -0,0 +1,106 @@
+/*
+ * Copyright 2019 Advanced Micro Devices, Inc.
+ *
+ * Permission is hereby granted, free of charge, to any person
+obtaining a
+ * copy of this software and associated documentation files (the
+"Software"),
+ * to deal in the Software without restriction, including without
+limitation
+ * the rights to use, copy, modify, merge, publish, distribute,
+sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom
+the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT
+SHALL
+ * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM,
+DAMAGES OR
+ * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+OTHERWISE,
+ * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE
+OR
+ * OTHER DEALINGS IN THE SOFTWARE.
+ *
+ */
+#include <linux/semaphore.h>
+#include <linux/atomic.h>
+
+/*
+ * Reusable 2 PHASE task barrier (randevouz point) implementation for N tasks.
+ * Based on the Little book of sempahores -
+https://greenteapress.com/wp/semaphores/
+ */
+
+
+
+#ifndef DRM_TASK_BARRIER_H_
+#define DRM_TASK_BARRIER_H_
+
[Le]: It might be better to prefix "drm_" to the functions and structure below, even this header file name.
+/*
+ * Represents an instance of a task barrier.
+ */
+struct task_barrier {
+ unsigned int n;
[Le]: We can define it as signed type here for more common use.
+ atomic_t count;
+ struct semaphore enter_turnstile;
+ struct semaphore exit_turnstile;
+};
+
+static inline void task_barrier_signal_turnstile(struct semaphore *turnstile,
+ unsigned int n)
+{
+ int i;
+
+ for (i = 0 ; i < n; i++)
+ up(turnstile);
+}
+
+static inline void task_barrier_init(struct task_barrier *tb) {
+ tb->n = 0;
+ atomic_set(&tb->count, 0);
+ sema_init(&tb->enter_turnstile, 0);
+ sema_init(&tb->exit_turnstile, 0);
+}
+
+static inline void task_barrier_add_task(struct task_barrier *tb) {
+ tb->n++;
+}
+
+static inline void task_barrier_rem_task(struct task_barrier *tb) {
+ tb->n--;
+}
+
+/*
+ * Lines up all the threads BEFORE the critical point.
+ *
+ * When all thread passed this code the entry barrier is back to locked state.
+ */
+static inline void task_barrier_enter(struct task_barrier *tb) {
+ if (atomic_inc_return(&tb->count) == tb->n)
+ task_barrier_signal_turnstile(&tb->enter_turnstile, tb->n);
+
+ down(&tb->enter_turnstile);
+}
+
+/*
+ * Lines up all the threads AFTER the critical point.
+ *
+ * This function is used to avoid any one thread running ahead of the
+reset if
[Le]: No need to mention "reset" here.
With the above addressed, Acked-by: Le Ma Le.Ma at amd.com<mailto:Le.Ma at amd.com>
Regards,
Ma Le
+ * the barrier is used in a loop (repeatedly) .
+ */
+static inline void task_barrier_exit(struct task_barrier *tb) {
+ if (atomic_dec_return(&tb->count) == 0)
+ task_barrier_signal_turnstile(&tb->exit_turnstile, tb->n);
+
+ down(&tb->exit_turnstile);
+}
+
+static inline void task_barrier_full(struct task_barrier *tb) {
+ task_barrier_enter(tb);
+ task_barrier_exit(tb);
+}
+
+#endif
--
2.7.4
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