on 11/24/2022 2:26 AM, Tejun Heo wrote:

On Wed, Nov 23, 2022 at 02:03:55PM +0800, Kemeng Shi wrote:

quoted

-static bool throtl_tg_can_upgrade(struct throtl_grp *tg)
+static bool throtl_tg_reach_low_limit(struct throtl_grp *tg, int rw)
 {
 	struct throtl_service_queue *sq = &tg->service_queue;
-	bool read_limit, write_limit;
+	bool limit = tg->bps[rw][LIMIT_LOW] || tg->iops[rw][LIMIT_LOW];
 
 	/*
 	 * if cgroup reaches low limit (if low limit is 0, the cgroup always
 	 * reaches), it's ok to upgrade to next limit
 	 */
-	read_limit = tg->bps[READ][LIMIT_LOW] || tg->iops[READ][LIMIT_LOW];
-	write_limit = tg->bps[WRITE][LIMIT_LOW] || tg->iops[WRITE][LIMIT_LOW];
-	if (!read_limit && !write_limit)
-		return true;
-	if (read_limit && sq->nr_queued[READ] &&
-	    (!write_limit || sq->nr_queued[WRITE]))
-		return true;
-	if (write_limit && sq->nr_queued[WRITE] &&
-	    (!read_limit || sq->nr_queued[READ]))
+	return !limit || sq->nr_queued[rw].
+}
+
+static bool throtl_tg_can_upgrade(struct throtl_grp *tg)
+{
+	if (throtl_tg_reach_low_limit(tg, READ) &&
+	    throtl_tg_reach_low_limit(tg, WRITE))

Are the conditions being checked actually equivalent? If so, can you
explicitly explain that these are equivalent conditions? If not, what are we
changing exactly?All replaced conditions to return true are as following:

condition 1
(!read_limit && !write_limit)
condition 2
read_limit && sq->nr_queued[READ] && (!write_limit || sq->nr_queued[WRITE])
condition 3
write_limit && sq->nr_queued[WRITE] && (!read_limit || sq->nr_queued[READ])

Transfering condition 2 as following:
read_limit && sq->nr_queued[READ] && (!write_limit || sq->nr_queued[WRITE])
is equivalent to
(read_limit && sq->nr_queued[READ]) &&
(!write_limit || (write_limit && sq->nr_queued[WRITE]))
is equivalent to
(read_limit && sq->nr_queued[READ] && !write_limit) ||
((read_limit && sq->nr_queued[READ] && (write_limit && sq->nr_queued[WRITE]))

Transfering condition 3 as following:
write_limit && sq->nr_queued[WRITE] && (!read_limit || sq->nr_queued[READ])
is equivalent to
(write_limit && sq->nr_queued[WRITE]) &&
(!read_limit || (read_limit && sq->nr_queued[READ]))
is equivalent to
((write_limit && sq->nr_queued[WRITE]) && !read_limit) ||
((write_limit && sq->nr_queued[WRITE]) && (read_limit && sq->nr_queued[READ]))

All replaced conditions to return true are collected as folloing:
condition 1.1
(!read_limit && !write_limit)
condition 1.2
(read_limit && sq->nr_queued[READ] && !write_limit)
condition 1.3
((read_limit && sq->nr_queued[READ] && (write_limit && sq->nr_queued[WRITE]))
condition 1.4
(write_limit && sq->nr_queued[WRITE]) && !read_limit)
condition 1.5 (the same as 1.3, can be ingored)
(write_limit && sq->nr_queued[WRITE]) && (read_limit && sq->nr_queued[READ]))

Condtions to return true in this patch is:
(!read_limit || (read_limit && sq->nr_queued[READ])) &&
(!write_limit || (write_limit && sq->nr_queued[WRITE]))
As "(a || b) && (c || d)" can be extracted to
(a && c) or (a && d) or (b && c) or (b && d ). So we can extract condtions to
condition 2.1
!read_limit && !write_limit
condition 2.2
!read_limit && (write_limit && sq->nr_queued[WRITE])
condition 2.3
(read_limit && sq->nr_queued[READ]) && !write_limit
condition 2.4
(read_limit && sq->nr_queued[READ]) && (write_limit && sq->nr_queued[WRITE])

Conditions match as following:
condition 1.1 = condition 2.1
condition 1.2 = condition 2.3
condition 1.3 = condition 2.4
condition 1.4 = condition 2.2

-- 
Best wishes
Kemeng Shi