// 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; stall_thrs = READ_ONCE(dql->stall_thrs); 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; bool all_prev_completed; num_queued = READ_ONCE(dql->num_queued); /* 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 = dql->last_obj_cnt; dql->num_completed = completed; dql->prev_num_queued = num_queued; dql_check_stall(dql);}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);
// 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;
stall_thrs = READ_ONCE(dql->stall_thrs);
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;
bool all_prev_completed;
num_queued = READ_ONCE(dql->num_queued);
/* 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 = dql->last_obj_cnt;
dql->num_completed = completed;
dql->prev_num_queued = num_queued;
dql_check_stall(dql);
}
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);