linux-kernel - [PATCH v4 32/58] dyndbg: refactor *dynamic_emit

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Message-ID: <20250803035816.603405-33-jim.cromie@gmail.com>
Date: Sat,  2 Aug 2025 21:57:50 -0600
From: Jim Cromie <jim.cromie@...il.com>
To: linux-kernel@...r.kernel.org,
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	gregkh@...uxfoundation.org,
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Subject: [PATCH v4 32/58] dyndbg: refactor *dynamic_emit_prefix to split lookups

Split dynamic_emit_prefix():

1. keep dynamic_emit_prefix() static inline
   check ANY flags before calling 2

2. __dynamic_emit_prefix()
   prints [TID] or <intr> if +t flag
   check LOOKUP flags before calling 3

3. __dynamic_emit_lookup()
   prints 1+ of: module, function, src-file, line

Notes:

With 3 only called when needed, print the trailing whitespace
unconditionally, and drop the pos_after_tid var.

By doing TID in 2, 3's output is cacheable in principle.

A prefix cache would allow de-duplicating the redundant data in the
_ddebug tables, and replacing them with space-efficient storage which
is not fast enough for every-time pr_debugs, but would work to fill
the cache the 1st time its enabled and invoked.

Signed-off-by: Jim Cromie <jim.cromie@...il.com>
---
 lib/dynamic_debug.c | 40 +++++++++++++++++++++++++---------------
 1 file changed, 25 insertions(+), 15 deletions(-)

diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index c3e27637d9357..26261b5f99f05 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -824,19 +824,8 @@ static int remaining(int wrote)
 	return 0;
 }
 
-static char *__dynamic_emit_prefix(const struct _ddebug *desc, char *buf)
+static int __dynamic_emit_lookup(const struct _ddebug *desc, char *buf, int pos)
 {
-	int pos_after_tid;
-	int pos = 0;
-
-	if (desc->flags & _DPRINTK_FLAGS_INCL_TID) {
-		if (in_interrupt())
-			pos += snprintf(buf + pos, remaining(pos), "<intr> ");
-		else
-			pos += snprintf(buf + pos, remaining(pos), "[%d] ",
-					task_pid_vnr(current));
-	}
-	pos_after_tid = pos;
 	if (desc->flags & _DPRINTK_FLAGS_INCL_MODNAME)
 		pos += snprintf(buf + pos, remaining(pos), "%s:",
 				desc->modname);
@@ -849,8 +838,29 @@ static char *__dynamic_emit_prefix(const struct _ddebug *desc, char *buf)
 	if (desc->flags & _DPRINTK_FLAGS_INCL_LINENO)
 		pos += snprintf(buf + pos, remaining(pos), "%d:",
 				desc->lineno);
-	if (pos - pos_after_tid)
-		pos += snprintf(buf + pos, remaining(pos), " ");
+
+	/* we have a non-empty prefix, add trailing space */
+	if (remaining(pos))
+		buf[pos++] = ' ';
+
+	return pos;
+}
+
+static char *__dynamic_emit_prefix(struct _ddebug *desc, char *buf)
+{
+	int pos = 0;
+
+	if (desc->flags & _DPRINTK_FLAGS_INCL_TID) {
+		if (in_interrupt())
+			pos += snprintf(buf + pos, remaining(pos), "<intr> ");
+		else
+			pos += snprintf(buf + pos, remaining(pos), "[%d] ",
+					task_pid_vnr(current));
+	}
+
+	if (unlikely(desc->flags & _DPRINTK_FLAGS_INCL_LOOKUP))
+		pos += __dynamic_emit_lookup(desc, buf, pos);
+
 	if (pos >= PREFIX_SIZE)
 		buf[PREFIX_SIZE - 1] = '\0';
 
@@ -859,7 +869,7 @@ static char *__dynamic_emit_prefix(const struct _ddebug *desc, char *buf)
 
 static inline char *dynamic_emit_prefix(struct _ddebug *desc, char *buf)
 {
-	if (unlikely(desc->flags & _DPRINTK_FLAGS_INCL_ANY))
+	if (desc->flags & _DPRINTK_FLAGS_INCL_ANY)
 		return __dynamic_emit_prefix(desc, buf);
 	return buf;
 }
-- 
2.50.1