cachepc-linux

Fork of AMDESE/linux with modifications for CachePC side-channel attack
git clone https://git.sinitax.com/sinitax/cachepc-linux
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dynamic_queue_limits.c (4429B)

      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);