| /* SPDX-License-Identifier: GPL-2.0 */ |
| /* |
| * 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__ |
| |
| #include <asm/bug.h> |
| |
| 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->last_obj_cnt = count; |
| |
| /* We want to force a write first, so that cpu do not attempt |
| * to get cache line containing last_obj_cnt, num_queued, adj_limit |
| * in Shared state, but directly does a Request For Ownership |
| * It is only a hint, we use barrier() only. |
| */ |
| barrier(); |
| |
| dql->num_queued += count; |
| } |
| |
| /* Returns how many objects can be queued, < 0 indicates over limit. */ |
| static inline int dql_avail(const struct dql *dql) |
| { |
| return READ_ONCE(dql->adj_limit) - READ_ONCE(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 */ |
| void dql_init(struct dql *dql, unsigned int hold_time); |
| |
| #endif /* _KERNEL_ */ |
| |
| #endif /* _LINUX_DQL_H */ |