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Diffstat (limited to 'include/linux/dynamic_queue_limits.h')
| -rw-r--r-- | include/linux/dynamic_queue_limits.h | 97 |
1 files changed, 97 insertions, 0 deletions
diff --git a/include/linux/dynamic_queue_limits.h b/include/linux/dynamic_queue_limits.h new file mode 100644 index 00000000..5621547d --- /dev/null +++ b/include/linux/dynamic_queue_limits.h @@ -0,0 +1,97 @@ +/* + * Dynamic queue limits (dql) - Definitions + * + * Copyright (c) 2011, Tom Herbert <therbert@google.com> + * + * 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__ + +struct dql { + /* Fields accessed in enqueue path (dql_queued) */ + unsigned int num_queued; /* Total ever queued */ + unsigned int adj_limit; /* limit + num_completed */ + unsigned int last_obj_cnt; /* Count at last queuing */ + + /* Fields accessed only by completion path (dql_completed) */ + + unsigned int limit ____cacheline_aligned_in_smp; /* Current limit */ + unsigned int num_completed; /* Total ever completed */ + + unsigned int prev_ovlimit; /* Previous over limit */ + unsigned int prev_num_queued; /* Previous queue total */ + unsigned int prev_last_obj_cnt; /* Previous queuing cnt */ + + unsigned int lowest_slack; /* Lowest slack found */ + unsigned long slack_start_time; /* Time slacks seen */ + + /* Configuration */ + unsigned int max_limit; /* Max limit */ + unsigned int min_limit; /* Minimum limit */ + unsigned int slack_hold_time; /* Time to measure slack */ +}; + +/* Set some static maximums */ +#define DQL_MAX_OBJECT (UINT_MAX / 16) +#define DQL_MAX_LIMIT ((UINT_MAX / 2) - DQL_MAX_OBJECT) + +/* + * 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) +{ + BUG_ON(count > DQL_MAX_OBJECT); + + dql->num_queued += count; + dql->last_obj_cnt = count; +} + +/* Returns how many objects can be queued, < 0 indicates over limit. */ +static inline int dql_avail(const struct dql *dql) +{ + return dql->adj_limit - dql->num_queued; +} + +/* 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 */ +int dql_init(struct dql *dql, unsigned hold_time); + +#endif /* _KERNEL_ */ + +#endif /* _LINUX_DQL_H */ |