[Crash-utility] [PATCH] crash: symbols: Optimize kernel module pseudo-symbol matching overhead
In a modern Linux environment with numerous kernel modules loaded, the
crash utility must process and sort tens of thousands (often 50,000+) of
module symbols. The symbol sorting function (compare_syms) and module
loading loops frequently check for pseudo-symbols using macros like
MODULE_PSEUDO_SYMBOL(), MODULE_START(), and others.
These macros heavily rely on the STREQ()/STRNEQ() macros, which
internally expand to string_exists() checks followed by a full strcmp()
or strncmp(). Because these macros are evaluated millions of times during
module initialization and sorting (O(N log N) complexity), the function
call overhead of strcmp() becomes a noticeable performance bottleneck.
By explicitly checking the first character of the symbol name
(e.g., (sp)->name[0] == '_') before invoking STRNEQ(), we introduce a
lightweight "early reject" mechanism. Since most regular module symbols
do not start with an underscore, this short-circuits the evaluation for
the vast majority of symbols, completely avoiding the overhead of
strncmp() macro expansion.
Additionally, since the symbol name could potentially be NULL, we safely
guard the character access with an explicit non-null check
((sp)->name &&) to prevent segmentation faults.
This patch applies the early reject optimization to:
1. All MODULE_* pseudo-symbol macros.
2. The compare_syms() function for "__insmod" and "_MODULE_START_"
checks.
This cumulative optimization yields a measurable performance improvement
in module symbol sorting and initialization speed.
Signed-off-by: Rui Qi <qirui.001(a)bytedance.com>
---
symbols.c | 20 ++++++++++----------
1 file changed, 10 insertions(+), 10 deletions(-)
diff --git a/symbols.c b/symbols.c
index 736d9d96d606..9b0de45e9a95 100644
--- a/symbols.c
+++ b/symbols.c
@@ -1314,14 +1314,14 @@ symname_hash_search(struct syment *table[], char *name)
* Output for sym -[lL] command.
*/
-#define MODULE_PSEUDO_SYMBOL(sp) (STRNEQ((sp)->name, "_MODULE_"))
+#define MODULE_PSEUDO_SYMBOL(sp) ((sp)->name && (sp)->name[0] ==
'_' && STRNEQ((sp)->name, "_MODULE_"))
-#define MODULE_START(sp) (STRNEQ((sp)->name, "_MODULE_START_"))
-#define MODULE_END(sp) (STRNEQ((sp)->name, "_MODULE_END_"))
-#define MODULE_INIT_START(sp) (STRNEQ((sp)->name, "_MODULE_INIT_START_"))
-#define MODULE_INIT_END(sp) (STRNEQ((sp)->name, "_MODULE_INIT_END_"))
-#define MODULE_SECTION_START(sp) (STRNEQ((sp)->name,
"_MODULE_SECTION_START"))
-#define MODULE_SECTION_END(sp) (STRNEQ((sp)->name,
"_MODULE_SECTION_END"))
+#define MODULE_START(sp) ((sp)->name && (sp)->name[0] == '_'
&& STRNEQ((sp)->name, "_MODULE_START_"))
+#define MODULE_END(sp) ((sp)->name && (sp)->name[0] == '_'
&& STRNEQ((sp)->name, "_MODULE_END_"))
+#define MODULE_INIT_START(sp) ((sp)->name && (sp)->name[0] == '_'
&& STRNEQ((sp)->name, "_MODULE_INIT_START_"))
+#define MODULE_INIT_END(sp) ((sp)->name && (sp)->name[0] == '_'
&& STRNEQ((sp)->name, "_MODULE_INIT_END_"))
+#define MODULE_SECTION_START(sp) ((sp)->name && (sp)->name[0] ==
'_' && STRNEQ((sp)->name, "_MODULE_SECTION_START"))
+#define MODULE_SECTION_END(sp) ((sp)->name && (sp)->name[0] ==
'_' && STRNEQ((sp)->name, "_MODULE_SECTION_END"))
#define MODULE_MEM_START(sp,t) (STRNEQ((sp)->name, module_tag[t].start))
#define MODULE_MEM_END(sp,t) (STRNEQ((sp)->name, module_tag[t].end))
@@ -3419,12 +3419,12 @@ compare_syms(const void *v1, const void *v2)
s2 = (struct syment *)v2;
if (s1->value == s2->value) {
- if (STRNEQ(s1->name, "__insmod"))
+ if (s1->name && s1->name[0] == '_' && STRNEQ(s1->name,
"__insmod"))
return -1;
- if (STRNEQ(s2->name, "__insmod"))
+ if (s2->name && s2->name[0] == '_' && STRNEQ(s2->name,
"__insmod"))
return 1;
if (MODULE_MEM_START(s2, MOD_TEXT) ||
- STRNEQ(s2->name, "_MODULE_START_"))
+ s2->name && s2->name[0] == '_' && STRNEQ(s2->name,
"_MODULE_START_"))
return 1;
/* Get pseudo section name. */
if (MODULE_SECTION_START(s1))
--
2.20.1