Re: Fix ia64 bit ops: Full barriers for bit operations returning

[Zoltan Menyhart <Zoltan.Menyhart@bull.net>]

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Christoph Lameter wrote:

> Could decomplicate this? Just use acquire / release and avoid the 
> additional intrinsics. The purpose is first of all correctness. Then we 
> can add some whiz bang on top. Also please sent patches inline not as 
> attachments.

I could have misunderstood what you wrote yesterday:

>>Could you consider using some cache hints, like "ld8.bias.nta"?
>>"bias" is a hint to acquire exclusive ownership.
>>"nta" is a hint to allocate the cache line only in L2
>>(and side effect: to bias it to be replaced).
>>All of the Itanium 2 processor's atomic instructions are handled
>>exclusively by the L2 cache.
> 
> Could you come up with a patch? Currently, I do not seem to be able to 
> spend enough time on it.

I thought you had asked for both the correct fencing and the cache hints.

Thanks,

Zoltan


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--- old/include/asm-ia64/bitops.h	2006-04-04 18:19:50.000000000 +0200
+++ linux-2.6.16/include/asm-ia64/bitops.h	2006-04-05 18:38:44.000000000 +0200
@@ -7,6 +7,11 @@
  *
  * 02/06/02 find_next_bit() and find_first_bit() added from Erich Focht's ia64 O(1)
  *	    scheduler patch
+ * 06/04/05 Added full fencing semantics to the atomic bit operations returning
+ *	    values.
+ *	    Note that it is a temporary solution while we are waiting for explicitly
+ *	    indicated fencing behavior, e.g.:
+ *			test_and_set_bit (int nr, void *addr, MODE_BARRIER)
  */
 
 #include <linux/compiler.h>
@@ -160,6 +165,7 @@ test_and_set_bit (int nr, volatile void 
 	volatile __u32 *m;
 	CMPXCHG_BUGCHECK_DECL
 
+	ia64_mf();
 	m = (volatile __u32 *) addr + (nr >> 5);
 	bit = 1 << (nr & 31);
 	do {
@@ -192,7 +198,7 @@ __test_and_set_bit (int nr, volatile voi
 
 /**
  * test_and_clear_bit - Clear a bit and return its old value
- * @nr: Bit to set
+ * @nr: Bit to clear
  * @addr: Address to count from
  *
  * This operation is atomic and cannot be reordered.  
@@ -205,6 +211,7 @@ test_and_clear_bit (int nr, volatile voi
 	volatile __u32 *m;
 	CMPXCHG_BUGCHECK_DECL
 
+	ia64_mf();
 	m = (volatile __u32 *) addr + (nr >> 5);
 	mask = ~(1 << (nr & 31));
 	do {
@@ -237,7 +244,7 @@ __test_and_clear_bit(int nr, volatile vo
 
 /**
  * test_and_change_bit - Change a bit and return its old value
- * @nr: Bit to set
+ * @nr: Bit to change
  * @addr: Address to count from
  *
  * This operation is atomic and cannot be reordered.  
@@ -250,6 +257,7 @@ test_and_change_bit (int nr, volatile vo
 	volatile __u32 *m;
 	CMPXCHG_BUGCHECK_DECL
 
+	ia64_mf();
 	m = (volatile __u32 *) addr + (nr >> 5);
 	bit = (1 << (nr & 31));
 	do {