1*75957ba3STom Herbert /* 2*75957ba3STom Herbert * Dynamic queue limits (dql) - Definitions 3*75957ba3STom Herbert * 4*75957ba3STom Herbert * Copyright (c) 2011, Tom Herbert <[email protected]> 5*75957ba3STom Herbert * 6*75957ba3STom Herbert * This header file contains the definitions for dynamic queue limits (dql). 7*75957ba3STom Herbert * dql would be used in conjunction with a producer/consumer type queue 8*75957ba3STom Herbert * (possibly a HW queue). Such a queue would have these general properties: 9*75957ba3STom Herbert * 10*75957ba3STom Herbert * 1) Objects are queued up to some limit specified as number of objects. 11*75957ba3STom Herbert * 2) Periodically a completion process executes which retires consumed 12*75957ba3STom Herbert * objects. 13*75957ba3STom Herbert * 3) Starvation occurs when limit has been reached, all queued data has 14*75957ba3STom Herbert * actually been consumed, but completion processing has not yet run 15*75957ba3STom Herbert * so queuing new data is blocked. 16*75957ba3STom Herbert * 4) Minimizing the amount of queued data is desirable. 17*75957ba3STom Herbert * 18*75957ba3STom Herbert * The goal of dql is to calculate the limit as the minimum number of objects 19*75957ba3STom Herbert * needed to prevent starvation. 20*75957ba3STom Herbert * 21*75957ba3STom Herbert * The primary functions of dql are: 22*75957ba3STom Herbert * dql_queued - called when objects are enqueued to record number of objects 23*75957ba3STom Herbert * dql_avail - returns how many objects are available to be queued based 24*75957ba3STom Herbert * on the object limit and how many objects are already enqueued 25*75957ba3STom Herbert * dql_completed - called at completion time to indicate how many objects 26*75957ba3STom Herbert * were retired from the queue 27*75957ba3STom Herbert * 28*75957ba3STom Herbert * The dql implementation does not implement any locking for the dql data 29*75957ba3STom Herbert * structures, the higher layer should provide this. dql_queued should 30*75957ba3STom Herbert * be serialized to prevent concurrent execution of the function; this 31*75957ba3STom Herbert * is also true for dql_completed. However, dql_queued and dlq_completed can 32*75957ba3STom Herbert * be executed concurrently (i.e. they can be protected by different locks). 33*75957ba3STom Herbert */ 34*75957ba3STom Herbert 35*75957ba3STom Herbert #ifndef _LINUX_DQL_H 36*75957ba3STom Herbert #define _LINUX_DQL_H 37*75957ba3STom Herbert 38*75957ba3STom Herbert #ifdef __KERNEL__ 39*75957ba3STom Herbert 40*75957ba3STom Herbert struct dql { 41*75957ba3STom Herbert /* Fields accessed in enqueue path (dql_queued) */ 42*75957ba3STom Herbert unsigned int num_queued; /* Total ever queued */ 43*75957ba3STom Herbert unsigned int adj_limit; /* limit + num_completed */ 44*75957ba3STom Herbert unsigned int last_obj_cnt; /* Count at last queuing */ 45*75957ba3STom Herbert 46*75957ba3STom Herbert /* Fields accessed only by completion path (dql_completed) */ 47*75957ba3STom Herbert 48*75957ba3STom Herbert unsigned int limit ____cacheline_aligned_in_smp; /* Current limit */ 49*75957ba3STom Herbert unsigned int num_completed; /* Total ever completed */ 50*75957ba3STom Herbert 51*75957ba3STom Herbert unsigned int prev_ovlimit; /* Previous over limit */ 52*75957ba3STom Herbert unsigned int prev_num_queued; /* Previous queue total */ 53*75957ba3STom Herbert unsigned int prev_last_obj_cnt; /* Previous queuing cnt */ 54*75957ba3STom Herbert 55*75957ba3STom Herbert unsigned int lowest_slack; /* Lowest slack found */ 56*75957ba3STom Herbert unsigned long slack_start_time; /* Time slacks seen */ 57*75957ba3STom Herbert 58*75957ba3STom Herbert /* Configuration */ 59*75957ba3STom Herbert unsigned int max_limit; /* Max limit */ 60*75957ba3STom Herbert unsigned int min_limit; /* Minimum limit */ 61*75957ba3STom Herbert unsigned int slack_hold_time; /* Time to measure slack */ 62*75957ba3STom Herbert }; 63*75957ba3STom Herbert 64*75957ba3STom Herbert /* Set some static maximums */ 65*75957ba3STom Herbert #define DQL_MAX_OBJECT (UINT_MAX / 16) 66*75957ba3STom Herbert #define DQL_MAX_LIMIT ((UINT_MAX / 2) - DQL_MAX_OBJECT) 67*75957ba3STom Herbert 68*75957ba3STom Herbert /* 69*75957ba3STom Herbert * Record number of objects queued. Assumes that caller has already checked 70*75957ba3STom Herbert * availability in the queue with dql_avail. 71*75957ba3STom Herbert */ 72*75957ba3STom Herbert static inline void dql_queued(struct dql *dql, unsigned int count) 73*75957ba3STom Herbert { 74*75957ba3STom Herbert BUG_ON(count > DQL_MAX_OBJECT); 75*75957ba3STom Herbert 76*75957ba3STom Herbert dql->num_queued += count; 77*75957ba3STom Herbert dql->last_obj_cnt = count; 78*75957ba3STom Herbert } 79*75957ba3STom Herbert 80*75957ba3STom Herbert /* Returns how many objects can be queued, < 0 indicates over limit. */ 81*75957ba3STom Herbert static inline int dql_avail(const struct dql *dql) 82*75957ba3STom Herbert { 83*75957ba3STom Herbert return dql->adj_limit - dql->num_queued; 84*75957ba3STom Herbert } 85*75957ba3STom Herbert 86*75957ba3STom Herbert /* Record number of completed objects and recalculate the limit. */ 87*75957ba3STom Herbert void dql_completed(struct dql *dql, unsigned int count); 88*75957ba3STom Herbert 89*75957ba3STom Herbert /* Reset dql state */ 90*75957ba3STom Herbert void dql_reset(struct dql *dql); 91*75957ba3STom Herbert 92*75957ba3STom Herbert /* Initialize dql state */ 93*75957ba3STom Herbert int dql_init(struct dql *dql, unsigned hold_time); 94*75957ba3STom Herbert 95*75957ba3STom Herbert #endif /* _KERNEL_ */ 96*75957ba3STom Herbert 97*75957ba3STom Herbert #endif /* _LINUX_DQL_H */ 98