mirror of
https://github.com/torvalds/linux.git
synced 2024-12-05 02:23:16 +00:00
4ba67ef3a1
With the previous change, struct dqs->stall_thrs will be in the hot path (at queue side), even if DQS is disabled. The other fields accessed in this function (last_obj_cnt and num_queued) are in the first cache line, let's move this field (stall_thrs) to the very first cache line, since there is a hole there. This does not change the structure size, since it moves an short (2 bytes) to 4-bytes whole in the first cache line. This is the new structure format now: struct dql { unsigned int num_queued; unsigned int last_obj_cnt; ... short unsigned int stall_thrs; /* XXX 2 bytes hole, try to pack */ ... /* --- cacheline 1 boundary (64 bytes) --- */ ... /* Longest stall detected, reported to user */ short unsigned int stall_max; /* XXX 2 bytes hole, try to pack */ }; Also, read the stall_thrs (now in the very first cache line) earlier, together with dql->num_queued (also in the first cache line). Suggested-by: Jakub Kicinski <kuba@kernel.org> Suggested-by: Eric Dumazet <edumazet@google.com> Signed-off-by: Breno Leitao <leitao@debian.org> Link: https://lore.kernel.org/r/20240411192241.2498631-5-leitao@debian.org Signed-off-by: Jakub Kicinski <kuba@kernel.org>
218 lines
6.6 KiB
C
218 lines
6.6 KiB
C
// 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 = 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);
|