diff options
| -rw-r--r-- | include/linux/dynamic_queue_limits.h | 97 | ||||
| -rw-r--r-- | lib/Kconfig | 3 | ||||
| -rw-r--r-- | lib/Makefile | 2 | ||||
| -rw-r--r-- | lib/dynamic_queue_limits.c | 133 |
4 files changed, 235 insertions, 0 deletions
diff --git a/include/linux/dynamic_queue_limits.h b/include/linux/dynamic_queue_limits.h new file mode 100644 index 00000000000..5621547d631 --- /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 */ diff --git a/lib/Kconfig b/lib/Kconfig index 32f3e5ae2be..63b5782732e 100644 --- a/lib/Kconfig +++ b/lib/Kconfig @@ -244,6 +244,9 @@ config CPU_RMAP bool depends on SMP +config DQL + bool + # # Netlink attribute parsing support is select'ed if needed # diff --git a/lib/Makefile b/lib/Makefile index a4da283f5dc..ff00d4dcb7e 100644 --- a/lib/Makefile +++ b/lib/Makefile @@ -115,6 +115,8 @@ obj-$(CONFIG_CPU_RMAP) += cpu_rmap.o obj-$(CONFIG_CORDIC) += cordic.o +obj-$(CONFIG_DQL) += dynamic_queue_limits.o + hostprogs-y := gen_crc32table clean-files := crc32table.h diff --git a/lib/dynamic_queue_limits.c b/lib/dynamic_queue_limits.c new file mode 100644 index 00000000000..3d1bdcdd7db --- /dev/null +++ b/lib/dynamic_queue_limits.c @@ -0,0 +1,133 @@ +/* + * Dynamic byte queue limits. See include/linux/dynamic_queue_limits.h + * + * Copyright (c) 2011, Tom Herbert <therbert@google.com> + */ +#include <linux/module.h> +#include <linux/types.h> +#include <linux/ctype.h> +#include <linux/kernel.h> +#include <linux/dynamic_queue_limits.h> + +#define POSDIFF(A, B) ((A) > (B) ? (A) - (B) : 0) + +/* Records completed count and recalculates the queue limit */ +void dql_completed(struct dql *dql, unsigned int count) +{ + unsigned int inprogress, prev_inprogress, limit; + unsigned int ovlimit, all_prev_completed, completed; + + /* Can't complete more than what's in queue */ + BUG_ON(count > dql->num_queued - dql->num_completed); + + completed = dql->num_completed + count; + limit = dql->limit; + ovlimit = POSDIFF(dql->num_queued - dql->num_completed, limit); + inprogress = dql->num_queued - completed; + prev_inprogress = dql->prev_num_queued - dql->num_completed; + all_prev_completed = POSDIFF(completed, dql->prev_num_queued); + + if ((ovlimit && !inprogress) || + (dql->prev_ovlimit && all_prev_completed)) { + /* + * Queue considered starved if: + * - The queue was over-limit in the last interval, + * and there is no more data in the queue. + * OR + * - The queue was over-limit in the previous interval and + * when enqueuing it was possible that all queued data + * had been consumed. This covers the case when queue + * may have becomes starved between completion processing + * running and next time enqueue was scheduled. + * + * When queue is starved increase the limit by the amount + * of bytes both sent and completed in the last interval, + * plus any previous over-limit. + */ + limit += POSDIFF(completed, dql->prev_num_queued) + + dql->prev_ovlimit; + dql->slack_start_time = jiffies; + dql->lowest_slack = UINT_MAX; + } else if (inprogress && prev_inprogress && !all_prev_completed) { + /* + * Queue was not starved, check if the limit can be decreased. + * A decrease is only considered if the queue has been busy in + * the whole interval (the check above). + * + * If there is slack, the amount of execess data queued above + * the the amount needed to prevent starvation, the queue limit + * can be decreased. To avoid hysteresis we consider the + * minimum amount of slack found over several iterations of the + * completion routine. + */ + unsigned int slack, slack_last_objs; + + /* + * Slack is the maximum of + * - The queue limit plus previous over-limit minus twice + * the number of objects completed. Note that two times + * number of completed bytes is a basis for an upper bound + * of the limit. + * - Portion of objects in the last queuing operation that + * was not part of non-zero previous over-limit. That is + * "round down" by non-overlimit portion of the last + * queueing operation. + */ + slack = POSDIFF(limit + dql->prev_ovlimit, + 2 * (completed - dql->num_completed)); + slack_last_objs = dql->prev_ovlimit ? + POSDIFF(dql->prev_last_obj_cnt, dql->prev_ovlimit) : 0; + + slack = max(slack, slack_last_objs); + + if (slack < dql->lowest_slack) + dql->lowest_slack = slack; + + if (time_after(jiffies, + dql->slack_start_time + dql->slack_hold_time)) { + limit = POSDIFF(limit, dql->lowest_slack); + dql->slack_start_time = jiffies; + dql->lowest_slack = UINT_MAX; + } + } + + /* Enforce bounds on limit */ + limit = clamp(limit, dql->min_limit, dql->max_limit); + + if (limit != dql->limit) { + dql->limit = limit; + ovlimit = 0; + } + + dql->adj_limit = limit + completed; + dql->prev_ovlimit = ovlimit; + dql->prev_last_obj_cnt = dql->last_obj_cnt; + dql->num_completed = completed; + dql->prev_num_queued = dql->num_queued; +} +EXPORT_SYMBOL(dql_completed); + +void dql_reset(struct dql *dql) +{ + /* Reset all dynamic values */ + dql->limit = 0; + dql->num_queued = 0; + dql->num_completed = 0; + dql->last_obj_cnt = 0; + dql->prev_num_queued = 0; + dql->prev_last_obj_cnt = 0; + dql->prev_ovlimit = 0; + dql->lowest_slack = UINT_MAX; + dql->slack_start_time = jiffies; +} +EXPORT_SYMBOL(dql_reset); + +int dql_init(struct dql *dql, unsigned hold_time) +{ + dql->max_limit = DQL_MAX_LIMIT; + dql->min_limit = 0; + dql->slack_hold_time = hold_time; + dql_reset(dql); + return 0; +} +EXPORT_SYMBOL(dql_init); |