Re: [PATCH -v7][RFC]: mutex: implement adaptive spinning

Ingo Molnar
2009-01-09T20:58:09Z

* Ingo Molnar <mingo@elte.hu> wrote:

> Note that meanwhile i also figured out why gcc got the inlining wrong
> there: the 'int nr' combined with the '% BITS_PER_LONG' signed
> arithmetics was too much for it to figure out at the inlining stage - it
> generated IDIV instructions, etc. With forced inlining later
> optimization stages managed to prove that the expression can be
> simplified.
>
> The second patch below that changes 'int nr' to 'unsigned nr' solves
> that problem, without the need to mark the function __always_inline.

The patch below that changes all the 'int nr' arguments to 'unsigned int
nr' in bitops.h and gives us a 0.3% size win (and all the right inlining
behavior) on x86 defconfig:

text data bss dec hex filename
6813470 1453188 801096 9067754 8a5cea vmlinux.before
6792602 1453188 801096 9046886 8a0b66 vmlinux.after

i checked other architectures and i can see many cases where the bitops
'nr' parameter is defined as unsigned - maybe they noticed this.

This change makes some sense anyway as a cleanup: a negative 'nr' bitop
argument does not make much sense IMO.

Ingo

---
arch/x86/include/asm/bitops.h | 31 ++++++++++++++++---------------
1 file changed, 16 insertions(+), 15 deletions(-)

Index: linux/arch/x86/include/asm/bitops.h
===================================================================
--- linux.orig/arch/x86/include/asm/bitops.h
+++ linux/arch/x86/include/asm/bitops.h
@@ -75,7 +75,7 @@ static inline void set_bit(unsigned int
* If it's called on the same region of memory simultaneously, the effect
* may be that only one operation succeeds.
*/
-static inline void __set_bit(int nr, volatile unsigned long *addr)
+static inline void __set_bit(unsigned int nr, volatile unsigned long *addr)
{
asm volatile("bts %1,%0" : ADDR : "Ir" (nr) : "memory");
}
@@ -90,7 +90,7 @@ static inline void __set_bit(int nr, vol
* you should call smp_mb__before_clear_bit() and/or smp_mb__after_clear_bit()
* in order to ensure changes are visible on other processors.
*/
-static inline void clear_bit(int nr, volatile unsigned long *addr)
+static inline void clear_bit(unsigned int nr, volatile unsigned long *addr)
{
if (IS_IMMEDIATE(nr)) {
asm volatile(LOCK_PREFIX "andb %1,%0"
@@ -117,7 +117,7 @@ static inline void clear_bit_unlock(unsi
clear_bit(nr, addr);
}

-static inline void __clear_bit(int nr, volatile unsigned long *addr)
+static inline void __clear_bit(unsigned int nr, volatile unsigned long *addr)
{
asm volatile("btr %1,%0" : ADDR : "Ir" (nr));
}
@@ -152,7 +152,7 @@ static inline void __clear_bit_unlock(un
* If it's called on the same region of memory simultaneously, the effect
* may be that only one operation succeeds.
*/
-static inline void __change_bit(int nr, volatile unsigned long *addr)
+static inline void __change_bit(unsigned int nr, volatile unsigned long *addr)
{
asm volatile("btc %1,%0" : ADDR : "Ir" (nr));
}
@@ -166,7 +166,7 @@ static inline void __change_bit(int nr,
* Note that @nr may be almost arbitrarily large; this function is not
* restricted to acting on a single-word quantity.
*/
-static inline void change_bit(int nr, volatile unsigned long *addr)
+static inline void change_bit(unsigned int nr, volatile unsigned long *addr)
{
if (IS_IMMEDIATE(nr)) {
asm volatile(LOCK_PREFIX "xorb %1,%0"
@@ -187,7 +187,7 @@ static inline void change_bit(int nr, vo
* This operation is atomic and cannot be reordered.
* It also implies a memory barrier.
*/
-static inline int test_and_set_bit(int nr, volatile unsigned long *addr)
+static inline int test_and_set_bit(unsigned int nr, volatile unsigned long *addr)
{
int oldbit;

@@ -204,7 +204,7 @@ static inline int test_and_set_bit(int n
*
* This is the same as test_and_set_bit on x86.
*/
-static inline int test_and_set_bit_lock(int nr, volatile unsigned long *addr)
+static inline int test_and_set_bit_lock(unsigned int nr, volatile unsigned long *addr)
{
return test_and_set_bit(nr, addr);
}
@@ -218,7 +218,7 @@ static inline int test_and_set_bit_lock(
* If two examples of this operation race, one can appear to succeed
* but actually fail. You must protect multiple accesses with a lock.
*/
-static inline int __test_and_set_bit(int nr, volatile unsigned long *addr)
+static inline int __test_and_set_bit(unsigned int nr, volatile unsigned long *addr)
{
int oldbit;

@@ -237,7 +237,7 @@ static inline int __test_and_set_bit(int
* This operation is atomic and cannot be reordered.
* It also implies a memory barrier.
*/
-static inline int test_and_clear_bit(int nr, volatile unsigned long *addr)
+static inline int test_and_clear_bit(unsigned int nr, volatile unsigned long *addr)
{
int oldbit;

@@ -257,7 +257,7 @@ static inline int test_and_clear_bit(int
* If two examples of this operation race, one can appear to succeed
* but actually fail. You must protect multiple accesses with a lock.
*/
-static inline int __test_and_clear_bit(int nr, volatile unsigned long *addr)
+static inline int __test_and_clear_bit(unsigned int nr, volatile unsigned long *addr)
{
int oldbit;

@@ -269,7 +269,7 @@ static inline int __test_and_clear_bit(i
}

/* WARNING: non atomic and it can be reordered! */
-static inline int __test_and_change_bit(int nr, volatile unsigned long *addr)
+static inline int __test_and_change_bit(unsigned int nr, volatile unsigned long *addr)
{
int oldbit;

@@ -289,7 +289,7 @@ static inline int __test_and_change_bit(
* This operation is atomic and cannot be reordered.
* It also implies a memory barrier.
*/
-static inline int test_and_change_bit(int nr, volatile unsigned long *addr)
+static inline int test_and_change_bit(unsigned int nr, volatile unsigned long *addr)
{
int oldbit;

@@ -300,13 +300,14 @@ static inline int test_and_change_bit(in
return oldbit;
}

-static inline int constant_test_bit(int nr, const volatile unsigned long *addr)
+static inline int
+constant_test_bit(unsigned int nr, const volatile unsigned long *addr)
{
return ((1UL << (nr % BITS_PER_LONG)) &
(((unsigned long *)addr)[nr / BITS_PER_LONG])) != 0;
}

-static inline int variable_test_bit(int nr, volatile const unsigned long *addr)
+static inline int variable_test_bit(unsigned int nr, volatile const unsigned long *addr)
{
int oldbit;

@@ -324,7 +325,7 @@ static inline int variable_test_bit(int
* @nr: bit number to test
* @addr: Address to start counting from
*/
-static int test_bit(int nr, const volatile unsigned long *addr);
+static int test_bit(unsigned int nr, const volatile unsigned long *addr);
#endif

#define test_bit(nr, addr) \