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From:   Jim Cromie <jim.cromie@gmail.com>
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        Jim Cromie <jim.cromie@gmail.com>
Subject: [PATCH v7c 20/24] dyndbg: refactor *dynamic_emit_prefix
Date:   Wed, 18 Oct 2023 11:06:00 -0600
Message-ID: <20231018170604.569042-21-jim.cromie@gmail.com>
In-Reply-To: <20231018170604.569042-1-jim.cromie@gmail.com>
References: <20231018170604.569042-1-jim.cromie@gmail.com>
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Precedence: bulk

Refactor the split of duties between outer & inner fns.

The outer fn was previously just an inline unlikely forward to inner,
which did all the work.

Now, outer handles +t and +l flags itself, and calls inner only when
_DPRINTK_FLAGS_INCL_LOOKUP is needed.

No functional change.

But it does make the results of the inner-fn more cache-friendly
(fewer entries, reused more often):

1- no spurious [TID] or <intr> noise
2- no LINE-number to bloat the cache (avg 9 pr_debugs/fn)
3- only LOOKUP stuff

Currently LOOKUPs are descriptor-field refs but could be replaced by
accessor functions.  This would allow the __dyndbg_sites section to be
de-duplicated and reclaimed; currently module, filename fields are
~90% repeated.  As the accessors get more expensive, the value of
caching part of the prefix goes up.

Also change inner-fn to return count of extra chars written to the
buffer, and drop "inline" from outer, let the compiler decide.  Maybe
also change name accordingly.

Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
---
fixup whitespace
---
 lib/dynamic_debug.c | 39 ++++++++++++++++++++++-----------------
 1 file changed, 22 insertions(+), 17 deletions(-)

diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index a6ee142668bf..9db797a0cf82 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -774,11 +774,28 @@ static int remaining(int wrote)
 	return 0;
 }
 
-static char *__dynamic_emit_prefix(const struct _ddebug *desc, char *buf)
+static int __dynamic_emit_prefix(const struct _ddebug *desc, char *buf, int pos)
+{
+	if (desc->flags & _DPRINTK_FLAGS_INCL_MODNAME)
+		pos += snprintf(buf + pos, remaining(pos), "%s:",
+				desc->modname);
+	if (desc->flags & _DPRINTK_FLAGS_INCL_FUNCNAME)
+		pos += snprintf(buf + pos, remaining(pos), "%s:",
+				desc->function);
+	if (desc->flags & _DPRINTK_FLAGS_INCL_SOURCENAME)
+		pos += snprintf(buf + pos, remaining(pos), "%s:",
+				trim_prefix(desc->filename));
+	return pos;
+}
+
+static char *dynamic_emit_prefix(struct _ddebug *desc, char *buf)
 {
 	int pos_after_tid;
 	int pos = 0;
 
+	if (likely(!(desc->flags & _DPRINTK_FLAGS_INCL_ANY)))
+		return buf;
+
 	if (desc->flags & _DPRINTK_FLAGS_INCL_TID) {
 		if (in_interrupt())
 			pos += snprintf(buf + pos, remaining(pos), "<intr> ");
@@ -787,15 +804,10 @@ static char *__dynamic_emit_prefix(const struct _ddebug *desc, char *buf)
 					task_pid_vnr(current));
 	}
 	pos_after_tid = pos;
-	if (desc->flags & _DPRINTK_FLAGS_INCL_MODNAME)
-		pos += snprintf(buf + pos, remaining(pos), "%s:",
-				desc->modname);
-	if (desc->flags & _DPRINTK_FLAGS_INCL_FUNCNAME)
-		pos += snprintf(buf + pos, remaining(pos), "%s:",
-				desc->function);
-	if (desc->flags & _DPRINTK_FLAGS_INCL_SOURCENAME)
-		pos += snprintf(buf + pos, remaining(pos), "%s:",
-				trim_prefix(desc->filename));
+
+	if (unlikely(desc->flags & _DPRINTK_FLAGS_INCL_LOOKUP))
+		pos += __dynamic_emit_prefix(desc, buf, pos);
+
 	if (desc->flags & _DPRINTK_FLAGS_INCL_LINENO)
 		pos += snprintf(buf + pos, remaining(pos), "%d:",
 				desc->lineno);
@@ -807,13 +819,6 @@ static char *__dynamic_emit_prefix(const struct _ddebug *desc, char *buf)
 	return buf;
 }
 
-static inline char *dynamic_emit_prefix(struct _ddebug *desc, char *buf)
-{
-	if (unlikely(desc->flags & _DPRINTK_FLAGS_INCL_ANY))
-		return __dynamic_emit_prefix(desc, buf);
-	return buf;
-}
-
 void __dynamic_pr_debug(struct _ddebug *descriptor, const char *fmt, ...)
 {
 	va_list args;
-- 
2.41.0