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From:   Jim Cromie <jim.cromie@gmail.com>
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        Jim Cromie <jim.cromie@gmail.com>
Subject: [PATCH v7b 20/25] dyndbg: add _DPRINTK_FLAGS_INCL_LOOKUP
Date:   Fri, 13 Oct 2023 16:48:12 -0600
Message-ID: <20231013224818.3456409-21-jim.cromie@gmail.com>
In-Reply-To: <20231013224818.3456409-1-jim.cromie@gmail.com>
References: <20231013224818.3456409-1-jim.cromie@gmail.com>
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dyndbg's dynamic prefixing (by +tmfsl flags) is needlessly expensive.

When an enabled (with +p) pr_debug is called, _DPRINTK_FLAGS_INCL_ANY
prefix decorations are sprintf'd into stack-mem for every call.

This string (or part of it) could be cached once its 1st generated,
and retrieved thereafter, as long as its deleted any time the
callsite's flags are changed afterwards.

So consider the prefix/decoration flags: 'tmfsl', and what should be
in the cache:

-t  thread-id. not part of the "callsite" info, derived from current.
    doesn't belong in the cache. it would be wrong.
    can be done in outer: dynamic_emit_prefix()

-l  line number
    this could be part of the prefix, but would bloat the cache
    can also be done in outer: dynamic_emit_prefix()

-mfs  module, function, source-file
    we cache these, composed into a sub-string.
    they are "lookups", currently to descriptor fields,
    could be accessor macros to "compressed" tables.
    cache saves more access work.

All enabled together, they compose a prefix string like:

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

So this patch extracts _DPRINTK_FLAGS_INCL_LOOKUP macro out of
_DPRINTK_FLAGS_INCL_ANY macro, then redefs latter.

Next re-refactor dynamic_emit_prefix inner/outer fns accordingly.

Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
---
 include/linux/dynamic_debug.h | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/include/linux/dynamic_debug.h b/include/linux/dynamic_debug.h
index 927cb14f24e0..2237d454bc19 100644
--- a/include/linux/dynamic_debug.h
+++ b/include/linux/dynamic_debug.h
@@ -40,10 +40,12 @@ 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 |\
+#define _DPRINTK_FLAGS_INCL_LOOKUP					\
+	(_DPRINTK_FLAGS_INCL_MODNAME | _DPRINTK_FLAGS_INCL_FUNCNAME |	\
 	 _DPRINTK_FLAGS_INCL_SOURCENAME)
+#define _DPRINTK_FLAGS_INCL_ANY						\
+	(_DPRINTK_FLAGS_INCL_LINENO | _DPRINTK_FLAGS_INCL_TID |		\
+	 _DPRINTK_FLAGS_INCL_LOOKUP)
 
 #if defined DEBUG
 #define _DPRINTK_FLAGS_DEFAULT _DPRINTK_FLAGS_PRINT
-- 
2.41.0