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v5.14.15
  1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 * Dynamic byte queue limits.  See include/linux/dynamic_queue_limits.h
  4 *
  5 * Copyright (c) 2011, Tom Herbert <therbert@google.com>
  6 */
  7#include <linux/types.h>
  8#include <linux/kernel.h>
  9#include <linux/jiffies.h>
 10#include <linux/dynamic_queue_limits.h>
 11#include <linux/compiler.h>
 12#include <linux/export.h>
 
 13
 14#define POSDIFF(A, B) ((int)((A) - (B)) > 0 ? (A) - (B) : 0)
 15#define AFTER_EQ(A, B) ((int)((A) - (B)) >= 0)
 16
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 17/* Records completed count and recalculates the queue limit */
 18void dql_completed(struct dql *dql, unsigned int count)
 19{
 20	unsigned int inprogress, prev_inprogress, limit;
 21	unsigned int ovlimit, completed, num_queued;
 
 22	bool all_prev_completed;
 23
 24	num_queued = READ_ONCE(dql->num_queued);
 
 
 
 
 
 
 25
 26	/* Can't complete more than what's in queue */
 27	BUG_ON(count > num_queued - dql->num_completed);
 28
 29	completed = dql->num_completed + count;
 30	limit = dql->limit;
 31	ovlimit = POSDIFF(num_queued - dql->num_completed, limit);
 32	inprogress = num_queued - completed;
 33	prev_inprogress = dql->prev_num_queued - dql->num_completed;
 34	all_prev_completed = AFTER_EQ(completed, dql->prev_num_queued);
 35
 36	if ((ovlimit && !inprogress) ||
 37	    (dql->prev_ovlimit && all_prev_completed)) {
 38		/*
 39		 * Queue considered starved if:
 40		 *   - The queue was over-limit in the last interval,
 41		 *     and there is no more data in the queue.
 42		 *  OR
 43		 *   - The queue was over-limit in the previous interval and
 44		 *     when enqueuing it was possible that all queued data
 45		 *     had been consumed.  This covers the case when queue
 46		 *     may have becomes starved between completion processing
 47		 *     running and next time enqueue was scheduled.
 48		 *
 49		 *     When queue is starved increase the limit by the amount
 50		 *     of bytes both sent and completed in the last interval,
 51		 *     plus any previous over-limit.
 52		 */
 53		limit += POSDIFF(completed, dql->prev_num_queued) +
 54		     dql->prev_ovlimit;
 55		dql->slack_start_time = jiffies;
 56		dql->lowest_slack = UINT_MAX;
 57	} else if (inprogress && prev_inprogress && !all_prev_completed) {
 58		/*
 59		 * Queue was not starved, check if the limit can be decreased.
 60		 * A decrease is only considered if the queue has been busy in
 61		 * the whole interval (the check above).
 62		 *
 63		 * If there is slack, the amount of excess data queued above
 64		 * the amount needed to prevent starvation, the queue limit
 65		 * can be decreased.  To avoid hysteresis we consider the
 66		 * minimum amount of slack found over several iterations of the
 67		 * completion routine.
 68		 */
 69		unsigned int slack, slack_last_objs;
 70
 71		/*
 72		 * Slack is the maximum of
 73		 *   - The queue limit plus previous over-limit minus twice
 74		 *     the number of objects completed.  Note that two times
 75		 *     number of completed bytes is a basis for an upper bound
 76		 *     of the limit.
 77		 *   - Portion of objects in the last queuing operation that
 78		 *     was not part of non-zero previous over-limit.  That is
 79		 *     "round down" by non-overlimit portion of the last
 80		 *     queueing operation.
 81		 */
 82		slack = POSDIFF(limit + dql->prev_ovlimit,
 83		    2 * (completed - dql->num_completed));
 84		slack_last_objs = dql->prev_ovlimit ?
 85		    POSDIFF(dql->prev_last_obj_cnt, dql->prev_ovlimit) : 0;
 86
 87		slack = max(slack, slack_last_objs);
 88
 89		if (slack < dql->lowest_slack)
 90			dql->lowest_slack = slack;
 91
 92		if (time_after(jiffies,
 93			       dql->slack_start_time + dql->slack_hold_time)) {
 94			limit = POSDIFF(limit, dql->lowest_slack);
 95			dql->slack_start_time = jiffies;
 96			dql->lowest_slack = UINT_MAX;
 97		}
 98	}
 99
100	/* Enforce bounds on limit */
101	limit = clamp(limit, dql->min_limit, dql->max_limit);
102
103	if (limit != dql->limit) {
104		dql->limit = limit;
105		ovlimit = 0;
106	}
107
108	dql->adj_limit = limit + completed;
109	dql->prev_ovlimit = ovlimit;
110	dql->prev_last_obj_cnt = dql->last_obj_cnt;
111	dql->num_completed = completed;
112	dql->prev_num_queued = num_queued;
 
 
113}
114EXPORT_SYMBOL(dql_completed);
115
116void dql_reset(struct dql *dql)
117{
118	/* Reset all dynamic values */
119	dql->limit = 0;
120	dql->num_queued = 0;
121	dql->num_completed = 0;
122	dql->last_obj_cnt = 0;
123	dql->prev_num_queued = 0;
124	dql->prev_last_obj_cnt = 0;
125	dql->prev_ovlimit = 0;
126	dql->lowest_slack = UINT_MAX;
127	dql->slack_start_time = jiffies;
 
 
 
 
128}
129EXPORT_SYMBOL(dql_reset);
130
131void dql_init(struct dql *dql, unsigned int hold_time)
132{
133	dql->max_limit = DQL_MAX_LIMIT;
134	dql->min_limit = 0;
135	dql->slack_hold_time = hold_time;
 
136	dql_reset(dql);
137}
138EXPORT_SYMBOL(dql_init);
v6.13.7
  1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 * Dynamic byte queue limits.  See include/linux/dynamic_queue_limits.h
  4 *
  5 * Copyright (c) 2011, Tom Herbert <therbert@google.com>
  6 */
  7#include <linux/types.h>
  8#include <linux/kernel.h>
  9#include <linux/jiffies.h>
 10#include <linux/dynamic_queue_limits.h>
 11#include <linux/compiler.h>
 12#include <linux/export.h>
 13#include <trace/events/napi.h>
 14
 15#define POSDIFF(A, B) ((int)((A) - (B)) > 0 ? (A) - (B) : 0)
 16#define AFTER_EQ(A, B) ((int)((A) - (B)) >= 0)
 17
 18static void dql_check_stall(struct dql *dql, unsigned short stall_thrs)
 19{
 20	unsigned long now;
 21
 22	if (!stall_thrs)
 23		return;
 24
 25	now = jiffies;
 26	/* Check for a potential stall */
 27	if (time_after_eq(now, dql->last_reap + stall_thrs)) {
 28		unsigned long hist_head, t, start, end;
 29
 30		/* We are trying to detect a period of at least @stall_thrs
 31		 * jiffies without any Tx completions, but during first half
 32		 * of which some Tx was posted.
 33		 */
 34dqs_again:
 35		hist_head = READ_ONCE(dql->history_head);
 36		/* pairs with smp_wmb() in dql_queued() */
 37		smp_rmb();
 38
 39		/* Get the previous entry in the ring buffer, which is the
 40		 * oldest sample.
 41		 */
 42		start = (hist_head - DQL_HIST_LEN + 1) * BITS_PER_LONG;
 43
 44		/* Advance start to continue from the last reap time */
 45		if (time_before(start, dql->last_reap + 1))
 46			start = dql->last_reap + 1;
 47
 48		/* Newest sample we should have already seen a completion for */
 49		end = hist_head * BITS_PER_LONG + (BITS_PER_LONG - 1);
 50
 51		/* Shrink the search space to [start, (now - start_thrs/2)] if
 52		 * `end` is beyond the stall zone
 53		 */
 54		if (time_before(now, end + stall_thrs / 2))
 55			end = now - stall_thrs / 2;
 56
 57		/* Search for the queued time in [t, end] */
 58		for (t = start; time_before_eq(t, end); t++)
 59			if (test_bit(t % (DQL_HIST_LEN * BITS_PER_LONG),
 60				     dql->history))
 61				break;
 62
 63		/* Variable t contains the time of the queue */
 64		if (!time_before_eq(t, end))
 65			goto no_stall;
 66
 67		/* The ring buffer was modified in the meantime, retry */
 68		if (hist_head != READ_ONCE(dql->history_head))
 69			goto dqs_again;
 70
 71		dql->stall_cnt++;
 72		dql->stall_max = max_t(unsigned short, dql->stall_max, now - t);
 73
 74		trace_dql_stall_detected(dql->stall_thrs, now - t,
 75					 dql->last_reap, dql->history_head,
 76					 now, dql->history);
 77	}
 78no_stall:
 79	dql->last_reap = now;
 80}
 81
 82/* Records completed count and recalculates the queue limit */
 83void dql_completed(struct dql *dql, unsigned int count)
 84{
 85	unsigned int inprogress, prev_inprogress, limit;
 86	unsigned int ovlimit, completed, num_queued;
 87	unsigned short stall_thrs;
 88	bool all_prev_completed;
 89
 90	num_queued = READ_ONCE(dql->num_queued);
 91	/* Read stall_thrs in advance since it belongs to the same (first)
 92	 * cache line as ->num_queued. This way, dql_check_stall() does not
 93	 * need to touch the first cache line again later, reducing the window
 94	 * of possible false sharing.
 95	 */
 96	stall_thrs = READ_ONCE(dql->stall_thrs);
 97
 98	/* Can't complete more than what's in queue */
 99	BUG_ON(count > num_queued - dql->num_completed);
100
101	completed = dql->num_completed + count;
102	limit = dql->limit;
103	ovlimit = POSDIFF(num_queued - dql->num_completed, limit);
104	inprogress = num_queued - completed;
105	prev_inprogress = dql->prev_num_queued - dql->num_completed;
106	all_prev_completed = AFTER_EQ(completed, dql->prev_num_queued);
107
108	if ((ovlimit && !inprogress) ||
109	    (dql->prev_ovlimit && all_prev_completed)) {
110		/*
111		 * Queue considered starved if:
112		 *   - The queue was over-limit in the last interval,
113		 *     and there is no more data in the queue.
114		 *  OR
115		 *   - The queue was over-limit in the previous interval and
116		 *     when enqueuing it was possible that all queued data
117		 *     had been consumed.  This covers the case when queue
118		 *     may have becomes starved between completion processing
119		 *     running and next time enqueue was scheduled.
120		 *
121		 *     When queue is starved increase the limit by the amount
122		 *     of bytes both sent and completed in the last interval,
123		 *     plus any previous over-limit.
124		 */
125		limit += POSDIFF(completed, dql->prev_num_queued) +
126		     dql->prev_ovlimit;
127		dql->slack_start_time = jiffies;
128		dql->lowest_slack = UINT_MAX;
129	} else if (inprogress && prev_inprogress && !all_prev_completed) {
130		/*
131		 * Queue was not starved, check if the limit can be decreased.
132		 * A decrease is only considered if the queue has been busy in
133		 * the whole interval (the check above).
134		 *
135		 * If there is slack, the amount of excess data queued above
136		 * the amount needed to prevent starvation, the queue limit
137		 * can be decreased.  To avoid hysteresis we consider the
138		 * minimum amount of slack found over several iterations of the
139		 * completion routine.
140		 */
141		unsigned int slack, slack_last_objs;
142
143		/*
144		 * Slack is the maximum of
145		 *   - The queue limit plus previous over-limit minus twice
146		 *     the number of objects completed.  Note that two times
147		 *     number of completed bytes is a basis for an upper bound
148		 *     of the limit.
149		 *   - Portion of objects in the last queuing operation that
150		 *     was not part of non-zero previous over-limit.  That is
151		 *     "round down" by non-overlimit portion of the last
152		 *     queueing operation.
153		 */
154		slack = POSDIFF(limit + dql->prev_ovlimit,
155		    2 * (completed - dql->num_completed));
156		slack_last_objs = dql->prev_ovlimit ?
157		    POSDIFF(dql->prev_last_obj_cnt, dql->prev_ovlimit) : 0;
158
159		slack = max(slack, slack_last_objs);
160
161		if (slack < dql->lowest_slack)
162			dql->lowest_slack = slack;
163
164		if (time_after(jiffies,
165			       dql->slack_start_time + dql->slack_hold_time)) {
166			limit = POSDIFF(limit, dql->lowest_slack);
167			dql->slack_start_time = jiffies;
168			dql->lowest_slack = UINT_MAX;
169		}
170	}
171
172	/* Enforce bounds on limit */
173	limit = clamp(limit, dql->min_limit, dql->max_limit);
174
175	if (limit != dql->limit) {
176		dql->limit = limit;
177		ovlimit = 0;
178	}
179
180	dql->adj_limit = limit + completed;
181	dql->prev_ovlimit = ovlimit;
182	dql->prev_last_obj_cnt = READ_ONCE(dql->last_obj_cnt);
183	dql->num_completed = completed;
184	dql->prev_num_queued = num_queued;
185
186	dql_check_stall(dql, stall_thrs);
187}
188EXPORT_SYMBOL(dql_completed);
189
190void dql_reset(struct dql *dql)
191{
192	/* Reset all dynamic values */
193	dql->limit = 0;
194	dql->num_queued = 0;
195	dql->num_completed = 0;
196	dql->last_obj_cnt = 0;
197	dql->prev_num_queued = 0;
198	dql->prev_last_obj_cnt = 0;
199	dql->prev_ovlimit = 0;
200	dql->lowest_slack = UINT_MAX;
201	dql->slack_start_time = jiffies;
202
203	dql->last_reap = jiffies;
204	dql->history_head = jiffies / BITS_PER_LONG;
205	memset(dql->history, 0, sizeof(dql->history));
206}
207EXPORT_SYMBOL(dql_reset);
208
209void dql_init(struct dql *dql, unsigned int hold_time)
210{
211	dql->max_limit = DQL_MAX_LIMIT;
212	dql->min_limit = 0;
213	dql->slack_hold_time = hold_time;
214	dql->stall_thrs = 0;
215	dql_reset(dql);
216}
217EXPORT_SYMBOL(dql_init);