Re: [PATCH] Fix WARN_ON / WARN_ON_ONCE regression

Andrew James Wade
2006-10-04T04:06:36Z

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@gmail.com>
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); \
})