lkml.org 
[lkml]   [2005]   [Jan]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectHorrible regression with -CURRENT from "Don't busy-lock-loop in preemptable spinlocks" patch
Linus,

The change below is causing major problems for me on a dual K7 with
CONFIG_PREEMPT enabled (cset -x and rebuilding makes the machine
usable again).

This change was merged a couple of days ago so I'm surprised nobody
else has reported this. I tried to find where this patch came from
but I don't see it on lkml only the bk history.

Note, even with this removed I'm still seeing a few (many actually)
"BUG: using smp_processor_id() in preemptible [00000001] code: xxx"
messages which I've not seen before --- that might be unrelated but I
do see *many* such messages so I'm sure I would have noticed this
before or it would have broken something earlier.

Is this specific to the k7 or do other people also see this?



Thanks,

--cw

---

# This is a BitKeeper generated diff -Nru style patch.
#
# ChangeSet
# 2005/01/15 09:40:45-08:00 mingo@elte.hu
# [PATCH] Don't busy-lock-loop in preemptable spinlocks
#
# Paul Mackerras points out that doing the _raw_spin_trylock each time
# through the loop will generate tons of unnecessary bus traffic.
# Instead, after we fail to get the lock we should poll it with simple
# loads until we see that it is clear and then retry the atomic op.
# Assuming a reasonable cache design, the loads won't generate any bus
# traffic until another cpu writes to the cacheline containing the lock.
#
# Agreed.
#
# Signed-off-by: Ingo Molnar <mingo@elte.hu>
# Signed-off-by: Linus Torvalds <torvalds@osdl.org>
#
# kernel/spinlock.c
# 2005/01/14 16:00:00-08:00 mingo@elte.hu +8 -6
# Don't busy-lock-loop in preemptable spinlocks
#
diff -Nru a/kernel/spinlock.c b/kernel/spinlock.c
--- a/kernel/spinlock.c 2005-01-16 21:43:15 -08:00
+++ b/kernel/spinlock.c 2005-01-16 21:43:15 -08:00
@@ -173,7 +173,7 @@
* (We do this in a function because inlining it would be excessive.)
*/

-#define BUILD_LOCK_OPS(op, locktype) \
+#define BUILD_LOCK_OPS(op, locktype, is_locked_fn) \
void __lockfunc _##op##_lock(locktype *lock) \
{ \
preempt_disable(); \
@@ -183,7 +183,8 @@
preempt_enable(); \
if (!(lock)->break_lock) \
(lock)->break_lock = 1; \
- cpu_relax(); \
+ while (is_locked_fn(lock) && (lock)->break_lock) \
+ cpu_relax(); \
preempt_disable(); \
} \
} \
@@ -204,7 +205,8 @@
preempt_enable(); \
if (!(lock)->break_lock) \
(lock)->break_lock = 1; \
- cpu_relax(); \
+ while (is_locked_fn(lock) && (lock)->break_lock) \
+ cpu_relax(); \
preempt_disable(); \
} \
return flags; \
@@ -244,9 +246,9 @@
* _[spin|read|write]_lock_irqsave()
* _[spin|read|write]_lock_bh()
*/
-BUILD_LOCK_OPS(spin, spinlock_t);
-BUILD_LOCK_OPS(read, rwlock_t);
-BUILD_LOCK_OPS(write, rwlock_t);
+BUILD_LOCK_OPS(spin, spinlock_t, spin_is_locked);
+BUILD_LOCK_OPS(read, rwlock_t, rwlock_is_locked);
+BUILD_LOCK_OPS(write, rwlock_t, spin_is_locked);

#endif /* CONFIG_PREEMPT */

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
\
 
 \ /
  Last update: 2005-03-22 14:09    [W:0.107 / U:7.064 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site