Hello.
Ralf Baechle wrote:
It was a nice optimization - on paper at least. In practice it results in
branches that may exceed the maximum legal range for a branch. We can
fight that problem with -ffunction-sections but -ffunction-sections again
is incompatible with -pg used by the function tracer.
By rewriting the loop around all simple LL/SC blocks to C we reduce reduce
the amount of inline assembler and at the same time allow GCC to often
fill the branch delay slots with something sensible or whever else clever
^^^^^^
Whichever?
optimization it may have up in its sleeve.
With this optimization gone we also no longer need -ffunction-sections,
so drop it.
This optimization was originall introduced in 2.6.21, commit
^^^^^^^^^
Originally.
5999eca25c1fd4b9b9aca7833b04d10fe4bc877d (linux-mips.org) rsp.
f65e4fa8e0c6022ad58dc88d1b11b12589ed7f9f (kernel.org).
Original fix for the issues which caused me to pull this optimization by
Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>.
Signed-off-by: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
Index: linux-queue/arch/mips/include/asm/atomic.h
===================================================================
--- linux-queue.orig/arch/mips/include/asm/atomic.h
+++ linux-queue/arch/mips/include/asm/atomic.h
[...]
@@ -443,18 +436,16 @@ static __inline__ void atomic64_add(long
} else if (kernel_uses_llsc) {
long temp;
- __asm__ __volatile__(
- " .set mips3 \n"
- "1: lld %0, %1 # atomic64_add \n"
- " daddu %0, %2 \n"
- " scd %0, %1 \n"
- " beqz %0, 2f \n"
- " .subsection 2 \n"
- "2: b 1b \n"
- " .previous \n"
- " .set mips0 \n"
- : "=&r" (temp), "=m" (v->counter)
- : "Ir" (i), "m" (v->counter));
+ do {
+ __asm__ __volatile__(
+ " .set mips3 \n"
+ "1: lld %0, %1 # atomic64_add \n"
You've kept the label here but it seems unused...
+ " daddu %0, %2 \n"
+ " scd %0, %1 \n"
+ " .set mips0 \n"
+ : "=&r" (temp), "=m" (v->counter)
+ : "Ir" (i), "m" (v->counter));
+ } while (unlikely(!temp));
} else {
unsigned long flags;
@@ -488,18 +479,16 @@ static __inline__ void atomic64_sub(long
} else if (kernel_uses_llsc) {
long temp;
- __asm__ __volatile__(
- " .set mips3 \n"
- "1: lld %0, %1 # atomic64_sub \n"
- " dsubu %0, %2 \n"
- " scd %0, %1 \n"
- " beqz %0, 2f \n"
- " .subsection 2 \n"
- "2: b 1b \n"
- " .previous \n"
- " .set mips0 \n"
- : "=&r" (temp), "=m" (v->counter)
- : "Ir" (i), "m" (v->counter));
+ do {
+ __asm__ __volatile__(
+ " .set mips3 \n"
+ "1: lld %0, %1 # atomic64_sub \n"
Same here...
+ " dsubu %0, %2 \n"
+ " scd %0, %1 \n"
+ " .set mips0 \n"
+ : "=&r" (temp), "=m" (v->counter)
+ : "Ir" (i), "m" (v->counter));
+ } while (unlikely(!temp));
} else {
unsigned long flags;
@@ -535,20 +524,19 @@ static __inline__ long atomic64_add_retu
} else if (kernel_uses_llsc) {
long temp;
- __asm__ __volatile__(
- " .set mips3 \n"
- "1: lld %1, %2 # atomic64_add_return \n"
- " daddu %0, %1, %3 \n"
- " scd %0, %2 \n"
- " beqz %0, 2f \n"
- " daddu %0, %1, %3 \n"
- " .subsection 2 \n"
- "2: b 1b \n"
- " .previous \n"
- " .set mips0 \n"
- : "=&r" (result), "=&r" (temp), "=m" (v->counter)
- : "Ir" (i), "m" (v->counter)
- : "memory");
+ do {
+ __asm__ __volatile__(
+ " .set mips3 \n"
+ "1: lld %1, %2 # atomic64_add_return \n"
... and here.
+ " daddu %0, %1, %3 \n"
+ " scd %0, %2 \n"
+ " .set mips0 \n"
+ : "=&r" (result), "=&r" (temp), "=m" (v->counter)
+ : "Ir" (i), "m" (v->counter)
+ : "memory");
+ } while (unlikely(!result));
+
+ result = temp + i;
} else {
unsigned long flags;
@@ -587,20 +575,19 @@ static __inline__ long atomic64_sub_retu
} else if (kernel_uses_llsc) {
long temp;
- __asm__ __volatile__(
- " .set mips3 \n"
- "1: lld %1, %2 # atomic64_sub_return \n"
- " dsubu %0, %1, %3 \n"
- " scd %0, %2 \n"
- " beqz %0, 2f \n"
- " dsubu %0, %1, %3 \n"
- " .subsection 2 \n"
- "2: b 1b \n"
- " .previous \n"
- " .set mips0 \n"
- : "=&r" (result), "=&r" (temp), "=m" (v->counter)
- : "Ir" (i), "m" (v->counter)
- : "memory");
+ do {
+ __asm__ __volatile__(
+ " .set mips3 \n"
+ "1: lld %1, %2 # atomic64_sub_return \n"
... and here.
+ " dsubu %0, %1, %3 \n"
+ " scd %0, %2 \n"
+ " .set mips0 \n"
+ : "=&r" (result), "=&r" (temp), "=m" (v->counter)
+ : "Ir" (i), "m" (v->counter)
+ : "memory");
+ } while (unlikely(!result));
+
+ result = temp - i;
} else {
unsigned long flags;
Index: linux-queue/arch/mips/include/asm/bitops.h
===================================================================
--- linux-queue.orig/arch/mips/include/asm/bitops.h
+++ linux-queue/arch/mips/include/asm/bitops.h
@@ -213,24 +205,22 @@ static inline void change_bit(unsigned l
" " __SC "%0, %1 \n"
" beqzl %0, 1b \n"
" .set mips0 \n"
- : "=&r" (temp), "=m" (*m)
- : "ir" (1UL << bit), "m" (*m));
+ : "=&r" (temp), "+m" (*m)
+ : "ir" (1UL << bit));
} else if (kernel_uses_llsc) {
unsigned long *m = ((unsigned long *) addr) + (nr >> SZLONG_LOG);
unsigned long temp;
- __asm__ __volatile__(
- " .set mips3 \n"
- "1: " __LL "%0, %1 # change_bit \n"
- " xor %0, %2 \n"
- " " __SC "%0, %1 \n"
- " beqz %0, 2f \n"
- " .subsection 2 \n"
- "2: b 1b \n"
- " .previous \n"
- " .set mips0 \n"
- : "=&r" (temp), "=m" (*m)
- : "ir" (1UL << bit), "m" (*m));
+ do {
+ __asm__ __volatile__(
+ " .set mips3 \n"
+ "1: " __LL "%0, %1 # change_bit \n"
... and here too.
+ " xor %0, %2 \n"
+ " " __SC "%0, %1 \n"
+ " .set mips0 \n"
+ : "=&r" (temp), "+m" (*m)
+ : "ir" (1UL << bit));
+ } while (unlikely(!temp));
} else {
volatile unsigned long *a = addr;
unsigned long mask;
@@ -272,30 +262,26 @@ static inline int test_and_set_bit(unsig
" beqzl %2, 1b \n"
" and %2, %0, %3 \n"
" .set mips0 \n"
- : "=&r" (temp), "=m" (*m), "=&r" (res)
- : "r" (1UL << bit), "m" (*m)
+ : "=&r" (temp), "+m" (*m), "=&r" (res)
+ : "r" (1UL << bit)
: "memory");
} else if (kernel_uses_llsc) {
unsigned long *m = ((unsigned long *) addr) + (nr >> SZLONG_LOG);
unsigned long temp;
- __asm__ __volatile__(
- " .set push \n"
- " .set noreorder \n"
- " .set mips3 \n"
- "1: " __LL "%0, %1 # test_and_set_bit \n"
- " or %2, %0, %3 \n"
- " " __SC "%2, %1 \n"
- " beqz %2, 2f \n"
- " and %2, %0, %3 \n"
- " .subsection 2 \n"
- "2: b 1b \n"
- " nop \n"
- " .previous \n"
- " .set pop \n"
- : "=&r" (temp), "=m" (*m), "=&r" (res)
- : "r" (1UL << bit), "m" (*m)
- : "memory");
+ do {
+ __asm__ __volatile__(
+ " .set mips3 \n"
+ "1: " __LL "%0, %1 # test_and_set_bit \n"
... and here as well.
+ " or %2, %0, %3 \n"
+ " " __SC "%2, %1 \n"
+ " .set mips0 \n"
+ : "=&r" (temp), "+m" (*m), "=&r" (res)
+ : "r" (1UL << bit)
+ : "memory");
+ } while (unlikely(!res));
+
+ res = temp & (1UL << bit);
} else {
volatile unsigned long *a = addr;
unsigned long mask;
@@ -340,30 +326,26 @@ static inline int test_and_set_bit_lock(
" beqzl %2, 1b \n"
" and %2, %0, %3 \n"
" .set mips0 \n"
- : "=&r" (temp), "=m" (*m), "=&r" (res)
- : "r" (1UL << bit), "m" (*m)
+ : "=&r" (temp), "+m" (*m), "=&r" (res)
+ : "r" (1UL << bit)
: "memory");
} else if (kernel_uses_llsc) {
unsigned long *m = ((unsigned long *) addr) + (nr >> SZLONG_LOG);
unsigned long temp;
- __asm__ __volatile__(
- " .set push \n"
- " .set noreorder \n"
- " .set mips3 \n"
- "1: " __LL "%0, %1 # test_and_set_bit \n"
- " or %2, %0, %3 \n"
- " " __SC "%2, %1 \n"
- " beqz %2, 2f \n"
- " and %2, %0, %3 \n"
- " .subsection 2 \n"
- "2: b 1b \n"
- " nop \n"
- " .previous \n"
- " .set pop \n"
- : "=&r" (temp), "=m" (*m), "=&r" (res)
- : "r" (1UL << bit), "m" (*m)
- : "memory");
+ do {
+ __asm__ __volatile__(
+ " .set mips3 \n"
+ "1: " __LL "%0, %1 # test_and_set_bit \n"
... and here.
+ " or %2, %0, %3 \n"
+ " " __SC "%2, %1 \n"
+ " .set mips0 \n"
+ : "=&r" (temp), "+m" (*m), "=&r" (res)
+ : "r" (1UL << bit)
+ : "memory");
+ } while(unlikely(!res));
+
+ res = temp & (1UL << bit);
} else {
volatile unsigned long *a = addr;
unsigned long mask;
@@ -410,49 +392,43 @@ static inline int test_and_clear_bit(uns
[...]
} else if (kernel_uses_llsc) {
unsigned long *m = ((unsigned long *) addr) + (nr >> SZLONG_LOG);
unsigned long temp;
- __asm__ __volatile__(
- " .set push \n"
- " .set noreorder \n"
- " .set mips3 \n"
- "1: " __LL "%0, %1 # test_and_clear_bit \n"
- " or %2, %0, %3 \n"
- " xor %2, %3 \n"
- " " __SC "%2, %1 \n"
- " beqz %2, 2f \n"
- " and %2, %0, %3 \n"
- " .subsection 2 \n"
- "2: b 1b \n"
- " nop \n"
- " .previous \n"
- " .set pop \n"
- : "=&r" (temp), "=m" (*m), "=&r" (res)
- : "r" (1UL << bit), "m" (*m)
- : "memory");
+ do {
+ __asm__ __volatile__(
+ " .set mips3 \n"
+ "1: " __LL "%0, %1 # test_and_clear_bit \n"
... and here.
+ " or %2, %0, %3 \n"
+ " xor %2, %3 \n"
+ " " __SC "%2, %1 \n"
+ " .set mips0 \n"
+ : "=&r" (temp), "+m" (*m), "=&r" (res)
+ : "r" (1UL << bit)
+ : "memory");
+ } while (unlikely(!res));
+
+ res = temp & (1UL << bit);
} else {
volatile unsigned long *a = addr;
unsigned long mask;
WBR, Sergei
