Re: [PATCH] Fix WARN_ON / WARN_ON_ONCE regression

On Tuesday 03 October 2006 21:14, Andrew Morton wrote:
There are changes here: in the old code we'll avoid reading the static
variable. In the new code we'll read the static variable, but we'll avoid
evaluating the condition.

Tim Chen's patch goes back to the old behaviour. I suspect the cache
misses on __warn_once is what he is measuring. If so, the (untested)
patch below should reduce the cache misses back to those of the old
code.

signed-off-by: Andrew Wade <andrew.j.wade@xxxxxxxxx>
diff -rupN a/include/asm-generic/bug.h b/include/asm-generic/bug.h
--- a/include/asm-generic/bug.h 2006-10-03 13:58:40.000000000 -0400
+++ b/include/asm-generic/bug.h 2006-10-03 23:17:37.000000000 -0400
@@ -45,9 +45,10 @@
static int __warn_once = 1; \
typeof(condition) __ret_warn_once = (condition);\
\
- if (likely(__warn_once)) \
- if (WARN_ON(__ret_warn_once)) \
+ if (unlikely(__ret_warn_once) && __warn_once) { \
__warn_once = 0; \
+ WARN_ON(1); \
+ }; \
unlikely(__ret_warn_once); \
})
-
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