linux-kernel - [PATCH v4 31/58] dyndbg: add _DPRINTK_FLAGS_INCL

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Message-ID: <20250803035816.603405-32-jim.cromie@gmail.com>
Date: Sat,  2 Aug 2025 21:57:49 -0600
From: Jim Cromie <jim.cromie@...il.com>
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Subject: [PATCH v4 31/58] dyndbg: add _DPRINTK_FLAGS_INCL_LOOKUP for +mfsl flags

dyndbg's dynamic prefixing can get expensive; each enabled callsite's
prefix is sprintf'd into stack-mem, every time a pr_debug is called.

A cache would help, if callsites mark _DPRINTK_FLAGS_PREFIX_CACHED
after saving the prefix string.  But not just yet.

_DPRINTK_FLAGS_INCL_LOOKUP distinguishes from _DPRINTK_FLAGS_INCL_ANY
by selecting *only* module,file,function fields to compose the
cacheable part of the (+tmfsl) dynamic prefix:

-t  thread-id. not part of the "callsite" info, its from current.
    doesn't belong in the cache. it would spoil it.
    do it in outer: dynamic_emit_prefix()

-mfs  module, function, source-file
    they are "lookups", currently to struct _ddebug fields.
    could be accessor macros to "compressed" tables.
    then they might be worth caching, ready for reuse.

-l  line
    this info could go either way.
    I elected to include it in LOOKUP, so in cache/inner fn.
    this makes cache larger but avoids sprintf %d each time.
    smaller cache needs smarter key.

All enabled together, they compose a prefix string like:

  # outer -----inner----------------------
  "[tid] module:function:sourcfile:line: "

So this patch extracts _DPRINTK_FLAGS_INCL_LOOKUP flags-combo out of
_DPRINTK_FLAGS_INCL_ANY, then redefs latter.

Next re-refactor dynamic_emit_prefix inner/outer fns accordingly.

Signed-off-by: Jim Cromie <jim.cromie@...il.com>
---
 include/linux/dynamic_debug.h | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/include/linux/dynamic_debug.h b/include/linux/dynamic_debug.h
index 0f7476456614e..d64f13a7a7394 100644
--- a/include/linux/dynamic_debug.h
+++ b/include/linux/dynamic_debug.h
@@ -40,10 +40,11 @@ struct _ddebug {
 #define _DPRINTK_FLAGS_INCL_SOURCENAME	(1<<5)
 #define _DPRINTK_FLAGS_PREFIX_CACHED	(1<<7)
 
-#define _DPRINTK_FLAGS_INCL_ANY		\
-	(_DPRINTK_FLAGS_INCL_MODNAME | _DPRINTK_FLAGS_INCL_FUNCNAME |\
-	 _DPRINTK_FLAGS_INCL_LINENO  | _DPRINTK_FLAGS_INCL_TID |\
-	 _DPRINTK_FLAGS_INCL_SOURCENAME)
+#define _DPRINTK_FLAGS_INCL_LOOKUP					\
+	(_DPRINTK_FLAGS_INCL_MODNAME | _DPRINTK_FLAGS_INCL_FUNCNAME |	\
+	 _DPRINTK_FLAGS_INCL_SOURCENAME | _DPRINTK_FLAGS_INCL_LINENO)
+#define _DPRINTK_FLAGS_INCL_ANY						\
+	(_DPRINTK_FLAGS_INCL_TID | _DPRINTK_FLAGS_INCL_LOOKUP)
 
 #if defined DEBUG
 #define _DPRINTK_FLAGS_DEFAULT _DPRINTK_FLAGS_PRINT
-- 
2.50.1