139 lines
4.3 KiB
C
Executable File
139 lines
4.3 KiB
C
Executable File
/*
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* Dynamic byte queue limits. See include/linux/dynamic_queue_limits.h
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*
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* Copyright (c) 2011, Tom Herbert <therbert@google.com>
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*/
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#include <linux/module.h>
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#include <linux/types.h>
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#include <linux/ctype.h>
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#include <linux/kernel.h>
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#include <linux/jiffies.h>
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#include <linux/dynamic_queue_limits.h>
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#define POSDIFF(A, B) ((int)((A) - (B)) > 0 ? (A) - (B) : 0)
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#define AFTER_EQ(A, B) ((int)((A) - (B)) >= 0)
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/* Records completed count and recalculates the queue limit */
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void dql_completed(struct dql *dql, unsigned int count)
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{
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unsigned int inprogress, prev_inprogress, limit;
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unsigned int ovlimit, completed, num_queued;
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bool all_prev_completed;
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num_queued = ACCESS_ONCE(dql->num_queued);
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/* Can't complete more than what's in queue */
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BUG_ON(count > num_queued - dql->num_completed);
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completed = dql->num_completed + count;
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limit = dql->limit;
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ovlimit = POSDIFF(num_queued - dql->num_completed, limit);
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inprogress = num_queued - completed;
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prev_inprogress = dql->prev_num_queued - dql->num_completed;
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all_prev_completed = AFTER_EQ(completed, dql->prev_num_queued);
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if ((ovlimit && !inprogress) ||
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(dql->prev_ovlimit && all_prev_completed)) {
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/*
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* Queue considered starved if:
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* - The queue was over-limit in the last interval,
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* and there is no more data in the queue.
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* OR
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* - The queue was over-limit in the previous interval and
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* when enqueuing it was possible that all queued data
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* had been consumed. This covers the case when queue
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* may have becomes starved between completion processing
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* running and next time enqueue was scheduled.
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*
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* When queue is starved increase the limit by the amount
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* of bytes both sent and completed in the last interval,
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* plus any previous over-limit.
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*/
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limit += POSDIFF(completed, dql->prev_num_queued) +
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dql->prev_ovlimit;
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dql->slack_start_time = jiffies;
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dql->lowest_slack = UINT_MAX;
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} else if (inprogress && prev_inprogress && !all_prev_completed) {
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/*
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* Queue was not starved, check if the limit can be decreased.
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* A decrease is only considered if the queue has been busy in
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* the whole interval (the check above).
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*
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* If there is slack, the amount of execess data queued above
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* the the amount needed to prevent starvation, the queue limit
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* can be decreased. To avoid hysteresis we consider the
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* minimum amount of slack found over several iterations of the
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* completion routine.
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*/
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unsigned int slack, slack_last_objs;
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/*
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* Slack is the maximum of
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* - The queue limit plus previous over-limit minus twice
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* the number of objects completed. Note that two times
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* number of completed bytes is a basis for an upper bound
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* of the limit.
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* - Portion of objects in the last queuing operation that
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* was not part of non-zero previous over-limit. That is
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* "round down" by non-overlimit portion of the last
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* queueing operation.
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*/
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slack = POSDIFF(limit + dql->prev_ovlimit,
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2 * (completed - dql->num_completed));
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slack_last_objs = dql->prev_ovlimit ?
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POSDIFF(dql->prev_last_obj_cnt, dql->prev_ovlimit) : 0;
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slack = max(slack, slack_last_objs);
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if (slack < dql->lowest_slack)
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dql->lowest_slack = slack;
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if (time_after(jiffies,
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dql->slack_start_time + dql->slack_hold_time)) {
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limit = POSDIFF(limit, dql->lowest_slack);
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dql->slack_start_time = jiffies;
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dql->lowest_slack = UINT_MAX;
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}
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}
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/* Enforce bounds on limit */
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limit = clamp(limit, dql->min_limit, dql->max_limit);
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if (limit != dql->limit) {
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dql->limit = limit;
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ovlimit = 0;
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}
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dql->adj_limit = limit + completed;
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dql->prev_ovlimit = ovlimit;
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dql->prev_last_obj_cnt = dql->last_obj_cnt;
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dql->num_completed = completed;
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dql->prev_num_queued = num_queued;
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}
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EXPORT_SYMBOL(dql_completed);
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void dql_reset(struct dql *dql)
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{
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/* Reset all dynamic values */
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dql->limit = 0;
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dql->num_queued = 0;
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dql->num_completed = 0;
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dql->last_obj_cnt = 0;
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dql->prev_num_queued = 0;
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dql->prev_last_obj_cnt = 0;
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dql->prev_ovlimit = 0;
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dql->lowest_slack = UINT_MAX;
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dql->slack_start_time = jiffies;
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}
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EXPORT_SYMBOL(dql_reset);
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int dql_init(struct dql *dql, unsigned hold_time)
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{
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dql->max_limit = DQL_MAX_LIMIT;
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dql->min_limit = 0;
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dql->slack_hold_time = hold_time;
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dql_reset(dql);
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return 0;
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}
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EXPORT_SYMBOL(dql_init);
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