// SPDX-License-Identifier: GPL-2.0/* * Dynamic byte queue limits.  See include/linux/dynamic_queue_limits.h * * Copyright (c) 2011, Tom Herbert <therbert@google.com> */#include <linux/types.h>#include <linux/kernel.h>#include <linux/jiffies.h>#include <linux/dynamic_queue_limits.h>#include <linux/compiler.h>#include <linux/export.h>#include <trace/events/napi.h> #define POSDIFF(A, B) ((int)((A) - (B)) > 0 ? (A) - (B) : 0)#define AFTER_EQ(A, B) ((int)((A) - (B)) >= 0) static void dql_check_stall(struct dql *dql, unsigned short stall_thrs){	unsigned long now; 	if (!stall_thrs)		return; 	now = jiffies;	/* Check for a potential stall */	if (time_after_eq(now, dql->last_reap + stall_thrs)) {		unsigned long hist_head, t, start, end; 		/* We are trying to detect a period of at least @stall_thrs		 * jiffies without any Tx completions, but during first half		 * of which some Tx was posted.		 */dqs_again:		hist_head = READ_ONCE(dql->history_head);		/* pairs with smp_wmb() in dql_queued() */		smp_rmb(); 		/* Get the previous entry in the ring buffer, which is the		 * oldest sample.		 */		start = (hist_head - DQL_HIST_LEN + 1) * BITS_PER_LONG; 		/* Advance start to continue from the last reap time */		if (time_before(start, dql->last_reap + 1))			start = dql->last_reap + 1; 		/* Newest sample we should have already seen a completion for */		end = hist_head * BITS_PER_LONG + (BITS_PER_LONG - 1); 		/* Shrink the search space to [start, (now - start_thrs/2)] if		 * `end` is beyond the stall zone		 */		if (time_before(now, end + stall_thrs / 2))			end = now - stall_thrs / 2; 		/* Search for the queued time in [t, end] */		for (t = start; time_before_eq(t, end); t++)			if (test_bit(t % (DQL_HIST_LEN * BITS_PER_LONG),				     dql->history))				break; 		/* Variable t contains the time of the queue */		if (!time_before_eq(t, end))			goto no_stall; 		/* The ring buffer was modified in the meantime, retry */		if (hist_head != READ_ONCE(dql->history_head))			goto dqs_again; 		dql->stall_cnt++;		dql->stall_max = max_t(unsigned short, dql->stall_max, now - t); 		trace_dql_stall_detected(dql->stall_thrs, now - t,					 dql->last_reap, dql->history_head,					 now, dql->history);	}no_stall:	dql->last_reap = now;} /* 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, completed, num_queued;	unsigned short stall_thrs;	bool all_prev_completed; 	num_queued = READ_ONCE(dql->num_queued);	/* Read stall_thrs in advance since it belongs to the same (first)	 * cache line as ->num_queued. This way, dql_check_stall() does not	 * need to touch the first cache line again later, reducing the window	 * of possible false sharing.	 */	stall_thrs = READ_ONCE(dql->stall_thrs); 	/* Can't complete more than what's in queue */	BUG_ON(count > num_queued - dql->num_completed); 	completed = dql->num_completed + count;	limit = dql->limit;	ovlimit = POSDIFF(num_queued - dql->num_completed, limit);	inprogress = num_queued - completed;	prev_inprogress = dql->prev_num_queued - dql->num_completed;	all_prev_completed = AFTER_EQ(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 excess data queued above		 * 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 = READ_ONCE(dql->last_obj_cnt);	dql->num_completed = completed;	dql->prev_num_queued = num_queued; 	dql_check_stall(dql, stall_thrs);}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; 	dql->last_reap = jiffies;	dql->history_head = jiffies / BITS_PER_LONG;	memset(dql->history, 0, sizeof(dql->history));}EXPORT_SYMBOL(dql_reset); void dql_init(struct dql *dql, unsigned int hold_time){	dql->max_limit = DQL_MAX_LIMIT;	dql->min_limit = 0;	dql->slack_hold_time = hold_time;	dql->stall_thrs = 0;	dql_reset(dql);}EXPORT_SYMBOL(dql_init);