linux-kernel - [PATCH] tools/lib/list_sort: Remove redundant code for cond

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Date: Sun, 26 May 2024 07:02:06 +0800
From: Kuan-Wei Chiu <visitorckw@...il.com>
To: akpm@...ux-foundation.org
Cc: peterz@...radead.org,
	mingo@...hat.com,
	acme@...nel.org,
	namhyung@...nel.org,
	mark.rutland@....com,
	alexander.shishkin@...ux.intel.com,
	jolsa@...nel.org,
	irogers@...gle.com,
	adrian.hunter@...el.com,
	kan.liang@...ux.intel.com,
	jserv@...s.ncku.edu.tw,
	linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Kuan-Wei Chiu <visitorckw@...il.com>
Subject: [PATCH] tools/lib/list_sort: Remove redundant code for cond_resched handling

Since cond_resched() is not called in userspace, remove the redundant
code in userspace's list_sort() implementation. This change eliminates
the unused 'count' variable and the associated logic for invoking cmp()
periodically, which was intended to trigger cond_resched() in kernel
space.

The removed code includes:
- Declaration and increment of the 'count' variable.
- Conditional invocation of cmp() based on 'count'.

This cleanup simplifies the merge_final function, avoids unnecessary
overhead, and has no impact on the functionality of list_sort() in
userspace.

Signed-off-by: Kuan-Wei Chiu <visitorckw@...il.com>
---
I've also Cc'd the maintainers and reviewers of the performance events
subsystem because the perf tool is the only user of userspace
list_sort().

 tools/lib/list_sort.c | 10 ----------
 1 file changed, 10 deletions(-)

diff --git a/tools/lib/list_sort.c b/tools/lib/list_sort.c
index 10c067e3a8d2..69affa251fa7 100644
--- a/tools/lib/list_sort.c
+++ b/tools/lib/list_sort.c
@@ -52,7 +52,6 @@ static void merge_final(void *priv, list_cmp_func_t cmp, struct list_head *head,
 			struct list_head *a, struct list_head *b)
 {
 	struct list_head *tail = head;
-	u8 count = 0;
 
 	for (;;) {
 		/* if equal, take 'a' -- important for sort stability */
@@ -78,15 +77,6 @@ static void merge_final(void *priv, list_cmp_func_t cmp, struct list_head *head,
 	/* Finish linking remainder of list b on to tail */
 	tail->next = b;
 	do {
-		/*
-		 * If the merge is highly unbalanced (e.g. the input is
-		 * already sorted), this loop may run many iterations.
-		 * Continue callbacks to the client even though no
-		 * element comparison is needed, so the client's cmp()
-		 * routine can invoke cond_resched() periodically.
-		 */
-		if (unlikely(!++count))
-			cmp(priv, b, b);
 		b->prev = tail;
 		tail = b;
 		b = b->next;
-- 
2.34.1