linux-kernel - [PATCH v7 21/25] dyndbg: refactor *dynamic_emit

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Message-ID: <20231012172137.3286566-22-jim.cromie@gmail.com>
Date:   Thu, 12 Oct 2023 11:21:32 -0600
From:   Jim Cromie <jim.cromie@...il.com>
To:     linux-kernel@...r.kernel.org, jbaron@...mai.com,
        gregkh@...uxfoundation.org, dri-devel@...ts.freedesktop.org,
        amd-gfx@...ts.freedesktop.org, intel-gvt-dev@...ts.freedesktop.org,
        intel-gfx@...ts.freedesktop.org
Cc:     daniel.vetter@...ll.ch, jani.nikula@...el.com,
        ville.syrjala@...ux.intel.com, seanpaul@...omium.org,
        robdclark@...il.com, groeck@...gle.com, yanivt@...gle.com,
        bleung@...gle.com, linux-doc@...r.kernel.org,
        Jim Cromie <jim.cromie@...il.com>
Subject: [PATCH v7 21/25] dyndbg: refactor *dynamic_emit_prefix

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@...il.com>
---
 lib/dynamic_debug.c | 55 ++++++++++++++++++++++++---------------------
 1 file changed, 30 insertions(+), 25 deletions(-)

diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index 17eefb35ac96..974395bf8a83 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -777,19 +777,8 @@ 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)
 {
-	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);
@@ -799,22 +788,38 @@ static char *__dynamic_emit_prefix(const struct _ddebug *desc, char *buf)
 	if (desc->flags & _DPRINTK_FLAGS_INCL_SOURCENAME)
 		pos += snprintf(buf + pos, remaining(pos), "%s:",
 				trim_prefix(desc->filename));
-	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), " ");
-	if (pos >= PREFIX_SIZE)
-		buf[PREFIX_SIZE - 1] = '\0';
-
-	return buf;
+	return pos;
 }
 
-static inline char *dynamic_emit_prefix(struct _ddebug *desc, char *buf)
+static 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;
+        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> ");
+                else
+                        pos += snprintf(buf + pos, remaining(pos), "[%d] ",
+                                        task_pid_vnr(current));
+        }
+        pos_after_tid = pos;
+
+        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);
+        if (pos - pos_after_tid)
+                pos += snprintf(buf + pos, remaining(pos), " ");
+        if (pos >= PREFIX_SIZE)
+                buf[PREFIX_SIZE - 1] = '\0';
+
+        return buf;
 }
 
 void __dynamic_pr_debug(struct _ddebug *descriptor, const char *fmt, ...)
-- 
2.41.0