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On PREEMPT_RT, rw_semaphores and rwlocks are substituted with an rtmutex and a reader count. The implementation is writer unfair, as it is not feasible to do priority inheritance on multiple readers, but experience has shown that real-time workloads are not the typical workloads which are sensitive to writer starvation. The inner workings of rw_semaphores and rwlocks on RT are almost identical except for the task state and signal handling. rw_semaphores are not state preserving over a contention, they are expected to enter and leave with state == TASK_RUNNING. rwlocks have a mechanism to preserve the state of the task at entry and restore it after unblocking taking potential non-lock related wakeups into account. rw_semaphores can also be subject to signal handling interrupting a blocked state, while rwlocks ignore signals. To avoid code duplication, provide a shared implementation which takes the small difference vs. state and signals into account. The code is included into the relevant rw_semaphore/rwlock base code and compiled for each use case separately. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://lore.kernel.org/r/20210815211302.957920571@linutronix.de
39 lines
876 B
C
39 lines
876 B
C
// SPDX-License-Identifier: GPL-2.0-only
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#ifndef _LINUX_RWBASE_RT_H
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#define _LINUX_RWBASE_RT_H
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#include <linux/rtmutex.h>
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#include <linux/atomic.h>
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#define READER_BIAS (1U << 31)
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#define WRITER_BIAS (1U << 30)
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struct rwbase_rt {
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atomic_t readers;
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struct rt_mutex_base rtmutex;
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};
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#define __RWBASE_INITIALIZER(name) \
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{ \
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.readers = ATOMIC_INIT(READER_BIAS), \
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.rtmutex = __RT_MUTEX_BASE_INITIALIZER(name.rtmutex), \
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}
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#define init_rwbase_rt(rwbase) \
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do { \
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rt_mutex_base_init(&(rwbase)->rtmutex); \
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atomic_set(&(rwbase)->readers, READER_BIAS); \
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} while (0)
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static __always_inline bool rw_base_is_locked(struct rwbase_rt *rwb)
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{
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return atomic_read(&rwb->readers) != READER_BIAS;
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}
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static __always_inline bool rw_base_is_contended(struct rwbase_rt *rwb)
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{
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return atomic_read(&rwb->readers) > 0;
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}
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#endif /* _LINUX_RWBASE_RT_H */
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