linux-kernel - [PATCH] Fix WARN_ON / WARN_ON

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Message-Id: <1159916644.8035.35.camel@localhost.localdomain>
Date:	Tue, 03 Oct 2006 16:04:04 -0700
From:	Tim Chen <tim.c.chen@...ux.intel.com>
To:	herbert@...dor.apana.org.au, akpm@...l.org
Cc:	linux-kernel@...r.kernel.org, leonid.ananiev@...el.com
Subject: [PATCH] Fix WARN_ON / WARN_ON_ONCE regression

Hi Herbet,

The patch "Let WARN_ON/WARN_ON_ONCE return the condition"
http://kernel.org/git/?
p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=684f978347deb42d180373ac4c427f82ef963171

introduced 40% more 2nd level cache miss to tbench workload
being run in a loop back mode on a Core 2 machine.  I think the
introduction of the local variables to WARN_ON and WARN_ON_ONCE

typeof(x) __ret_warn_on = (x);
typeof(condition) __ret_warn_once = (condition);

results in the extra cache misses.  In our test workload profile, we see
heavily used functions like do_softirq and local_bh_enable 
takes a lot longer to execute.  

The modification below helps fix the problem.  I made a slight
modification to sched.c to get around a gcc bug.

Signed-off-by: Tim Chen <tim.c.chen@...el.com>
diff --git a/include/asm-generic/bug.h b/include/asm-generic/bug.h
index a525089..05ed388 100644
--- a/include/asm-generic/bug.h
+++ b/include/asm-generic/bug.h
@@ -17,13 +17,12 @@ #endif
 
 #ifndef HAVE_ARCH_WARN_ON
 #define WARN_ON(condition)
({                                          \
-       typeof(condition) __ret_warn_on =
(condition);                  \
-       if (unlikely(__ret_warn_on))
{                                  \
+       if (unlikely(condition))
{                                      \
                printk("BUG: warning at %s:%d/%s()\n",
__FILE__,        \
                        __LINE__,
__FUNCTION__);                        \
                dump_stack
();                                           \
        }                                                               \
-       unlikely
(__ret_warn_on);                                        \
+       unlikely
(condition);                                            \
 })
 #endif
 
@@ -43,12 +42,16 @@ #endif
 
 #define WARN_ON_ONCE(condition)        ({                      \
        static int __warn_once = 1;                     \
-       typeof(condition) __ret_warn_once = (condition);\
                                                        \
-       if (likely(__warn_once))                        \
-               if (WARN_ON(__ret_warn_once))           \
-                       __warn_once = 0;                \
-       unlikely(__ret_warn_once);                      \
+       if (unlikely(condition)){                       \
+               if (likely(__warn_once)){               \
+                       __warn_once=0;                  \
+                       printk("BUG: warning at %s:%d/%s()\n", __FILE__,
\
+                               __LINE__, __FUNCTION__);\
+                       dump_stack();                   \
+               }                                       \
+       }                                               \
+       unlikely(condition);                            \
 })
 
 #ifdef CONFIG_SMP
diff --git a/kernel/sched.c b/kernel/sched.c
index 5c848fd..8ae972c 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -5629,7 +5629,8 @@ static unsigned long domain_distance(int
        struct sched_domain *sd;
 
        for_each_domain(cpu1, sd) {
-               WARN_ON(!cpu_isset(cpu1, sd->span));
+               if (unlikely(!cpu_isset(cpu1, sd->span)))
+                       WARN_ON(1);
                if (cpu_isset(cpu2, sd->span))
                        return distance;
                distance++;


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