/* SPDX-License-Identifier: GPL-2.0 */ /* * Dynamic queue limits (dql) - Definitions * * Copyright (c) 2011, Tom Herbert <[email protected]> * * This header file contains the definitions for dynamic queue limits (dql). * dql would be used in conjunction with a producer/consumer type queue * (possibly a HW queue). Such a queue would have these general properties: * * 1) Objects are queued up to some limit specified as number of objects. * 2) Periodically a completion process executes which retires consumed * objects. * 3) Starvation occurs when limit has been reached, all queued data has * actually been consumed, but completion processing has not yet run * so queuing new data is blocked. * 4) Minimizing the amount of queued data is desirable. * * The goal of dql is to calculate the limit as the minimum number of objects * needed to prevent starvation. * * The primary functions of dql are: * dql_queued - called when objects are enqueued to record number of objects * dql_avail - returns how many objects are available to be queued based * on the object limit and how many objects are already enqueued * dql_completed - called at completion time to indicate how many objects * were retired from the queue * * The dql implementation does not implement any locking for the dql data * structures, the higher layer should provide this. dql_queued should * be serialized to prevent concurrent execution of the function; this * is also true for dql_completed. However, dql_queued and dlq_completed can * be executed concurrently (i.e. they can be protected by different locks). */ #ifndef _LINUX_DQL_H #define _LINUX_DQL_H #ifdef __KERNEL__ #include <linux/bitops.h> #include <asm/bug.h> #define DQL_HIST_LEN … #define DQL_HIST_ENT(dql, idx) … struct dql { … }; /* Set some static maximums */ #define DQL_MAX_OBJECT … #define DQL_MAX_LIMIT … /* Populate the bitmap to be processed later in dql_check_stall() */ static inline void dql_queue_stall(struct dql *dql) { … } /* * Record number of objects queued. Assumes that caller has already checked * availability in the queue with dql_avail. */ static inline void dql_queued(struct dql *dql, unsigned int count) { … } /* Returns how many objects can be queued, < 0 indicates over limit. */ static inline int dql_avail(const struct dql *dql) { … } /* Record number of completed objects and recalculate the limit. */ void dql_completed(struct dql *dql, unsigned int count); /* Reset dql state */ void dql_reset(struct dql *dql); /* Initialize dql state */ void dql_init(struct dql *dql, unsigned int hold_time); #endif /* _KERNEL_ */ #endif /* _LINUX_DQL_H */
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