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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. v2: Remove mention of reset use case, improve doc. Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com> Reviewed-by: Le Ma <Le.Ma@amd.com> Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
108 lines
2.9 KiB
C
108 lines
2.9 KiB
C
/*
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* Copyright 2019 Advanced Micro Devices, Inc.
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*
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* Permission is hereby granted, free of charge, to any person obtaining a
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* copy of this software and associated documentation files (the "Software"),
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* to deal in the Software without restriction, including without limitation
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* the rights to use, copy, modify, merge, publish, distribute, sublicense,
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* and/or sell copies of the Software, and to permit persons to whom the
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* Software is furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
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* THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
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* OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
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* ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
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* OTHER DEALINGS IN THE SOFTWARE.
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*
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*/
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#include <linux/semaphore.h>
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#include <linux/atomic.h>
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/*
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* Reusable 2 PHASE task barrier (randevouz point) implementation for N tasks.
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* Based on the Little book of sempahores - https://greenteapress.com/wp/semaphores/
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*/
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#ifndef DRM_TASK_BARRIER_H_
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#define DRM_TASK_BARRIER_H_
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/*
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* Represents an instance of a task barrier.
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*/
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struct task_barrier {
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unsigned int n;
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atomic_t count;
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struct semaphore enter_turnstile;
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struct semaphore exit_turnstile;
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};
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static inline void task_barrier_signal_turnstile(struct semaphore *turnstile,
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unsigned int n)
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{
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int i;
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for (i = 0 ; i < n; i++)
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up(turnstile);
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}
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static inline void task_barrier_init(struct task_barrier *tb)
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{
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tb->n = 0;
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atomic_set(&tb->count, 0);
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sema_init(&tb->enter_turnstile, 0);
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sema_init(&tb->exit_turnstile, 0);
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}
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static inline void task_barrier_add_task(struct task_barrier *tb)
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{
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tb->n++;
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}
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static inline void task_barrier_rem_task(struct task_barrier *tb)
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{
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tb->n--;
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}
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/*
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* Lines up all the threads BEFORE the critical point.
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*
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* When all thread passed this code the entry barrier is back to locked state.
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*/
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static inline void task_barrier_enter(struct task_barrier *tb)
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{
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if (atomic_inc_return(&tb->count) == tb->n)
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task_barrier_signal_turnstile(&tb->enter_turnstile, tb->n);
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down(&tb->enter_turnstile);
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}
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/*
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* Lines up all the threads AFTER the critical point.
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*
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* This function is used to avoid any one thread running ahead if the barrier is
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* used repeatedly .
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*/
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static inline void task_barrier_exit(struct task_barrier *tb)
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{
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if (atomic_dec_return(&tb->count) == 0)
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task_barrier_signal_turnstile(&tb->exit_turnstile, tb->n);
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down(&tb->exit_turnstile);
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}
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/* Convinieince function when nothing to be done in between entry and exit */
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static inline void task_barrier_full(struct task_barrier *tb)
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{
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task_barrier_enter(tb);
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task_barrier_exit(tb);
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}
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#endif
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