MIPS: Optimize spinlocks.
The current locking mechanism uses a ll/sc sequence to release a
spinlock. This is slower than a wmb() followed by a store to unlock.
The branching forward to .subsection 2 on sc failure slows down the
contended case. So we get rid of that part too.
Since we are now working on naturally aligned u16 values, we can get
rid of a masking operation as the LHU already does the right thing.
The ANDI are reversed for better scheduling on multi-issue CPUs
On a 12 CPU 750MHz Octeon cn5750 this patch improves ipv4 UDP packet
forwarding rates from 3.58*10^6 PPS to 3.99*10^6 PPS, or about 11%.
Signed-off-by: David Daney <ddaney@caviumnetworks.com>
To: linux-mips@linux-mips.org
Patchwork: http://patchwork.linux-mips.org/patch/937/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/include/asm/spinlock.h b/arch/mips/include/asm/spinlock.h
index 5f16696..396e402 100644
--- a/arch/mips/include/asm/spinlock.h
+++ b/arch/mips/include/asm/spinlock.h
@@ -36,9 +36,9 @@
static inline int arch_spin_is_locked(arch_spinlock_t *lock)
{
- unsigned int counters = ACCESS_ONCE(lock->lock);
+ u32 counters = ACCESS_ONCE(lock->lock);
- return ((counters >> 14) ^ counters) & 0x1fff;
+ return ((counters >> 16) ^ counters) & 0xffff;
}
#define arch_spin_lock_flags(lock, flags) arch_spin_lock(lock)
@@ -47,9 +47,9 @@
static inline int arch_spin_is_contended(arch_spinlock_t *lock)
{
- unsigned int counters = ACCESS_ONCE(lock->lock);
+ u32 counters = ACCESS_ONCE(lock->lock);
- return (((counters >> 14) - counters) & 0x1fff) > 1;
+ return (((counters >> 16) - counters) & 0xffff) > 1;
}
#define arch_spin_is_contended arch_spin_is_contended
@@ -57,6 +57,7 @@
{
int my_ticket;
int tmp;
+ int inc = 0x10000;
if (R10000_LLSC_WAR) {
__asm__ __volatile__ (
@@ -64,25 +65,24 @@
" .set noreorder \n"
" \n"
"1: ll %[ticket], %[ticket_ptr] \n"
- " addiu %[my_ticket], %[ticket], 0x4000 \n"
+ " addu %[my_ticket], %[ticket], %[inc] \n"
" sc %[my_ticket], %[ticket_ptr] \n"
" beqzl %[my_ticket], 1b \n"
" nop \n"
- " srl %[my_ticket], %[ticket], 14 \n"
- " andi %[my_ticket], %[my_ticket], 0x1fff \n"
- " andi %[ticket], %[ticket], 0x1fff \n"
+ " srl %[my_ticket], %[ticket], 16 \n"
+ " andi %[ticket], %[ticket], 0xffff \n"
+ " andi %[my_ticket], %[my_ticket], 0xffff \n"
" bne %[ticket], %[my_ticket], 4f \n"
" subu %[ticket], %[my_ticket], %[ticket] \n"
"2: \n"
" .subsection 2 \n"
- "4: andi %[ticket], %[ticket], 0x1fff \n"
+ "4: andi %[ticket], %[ticket], 0xffff \n"
" sll %[ticket], 5 \n"
" \n"
"6: bnez %[ticket], 6b \n"
" subu %[ticket], 1 \n"
" \n"
- " lw %[ticket], %[ticket_ptr] \n"
- " andi %[ticket], %[ticket], 0x1fff \n"
+ " lhu %[ticket], %[serving_now_ptr] \n"
" beq %[ticket], %[my_ticket], 2b \n"
" subu %[ticket], %[my_ticket], %[ticket] \n"
" b 4b \n"
@@ -90,36 +90,33 @@
" .previous \n"
" .set pop \n"
: [ticket_ptr] "+m" (lock->lock),
+ [serving_now_ptr] "+m" (lock->h.serving_now),
[ticket] "=&r" (tmp),
- [my_ticket] "=&r" (my_ticket));
+ [my_ticket] "=&r" (my_ticket)
+ : [inc] "r" (inc));
} else {
__asm__ __volatile__ (
" .set push # arch_spin_lock \n"
" .set noreorder \n"
" \n"
- " ll %[ticket], %[ticket_ptr] \n"
- "1: addiu %[my_ticket], %[ticket], 0x4000 \n"
+ "1: ll %[ticket], %[ticket_ptr] \n"
+ " addu %[my_ticket], %[ticket], %[inc] \n"
" sc %[my_ticket], %[ticket_ptr] \n"
- " beqz %[my_ticket], 3f \n"
- " nop \n"
- " srl %[my_ticket], %[ticket], 14 \n"
- " andi %[my_ticket], %[my_ticket], 0x1fff \n"
- " andi %[ticket], %[ticket], 0x1fff \n"
+ " beqz %[my_ticket], 1b \n"
+ " srl %[my_ticket], %[ticket], 16 \n"
+ " andi %[ticket], %[ticket], 0xffff \n"
+ " andi %[my_ticket], %[my_ticket], 0xffff \n"
" bne %[ticket], %[my_ticket], 4f \n"
" subu %[ticket], %[my_ticket], %[ticket] \n"
"2: \n"
" .subsection 2 \n"
- "3: b 1b \n"
- " ll %[ticket], %[ticket_ptr] \n"
- " \n"
"4: andi %[ticket], %[ticket], 0x1fff \n"
" sll %[ticket], 5 \n"
" \n"
"6: bnez %[ticket], 6b \n"
" subu %[ticket], 1 \n"
" \n"
- " lw %[ticket], %[ticket_ptr] \n"
- " andi %[ticket], %[ticket], 0x1fff \n"
+ " lhu %[ticket], %[serving_now_ptr] \n"
" beq %[ticket], %[my_ticket], 2b \n"
" subu %[ticket], %[my_ticket], %[ticket] \n"
" b 4b \n"
@@ -127,8 +124,10 @@
" .previous \n"
" .set pop \n"
: [ticket_ptr] "+m" (lock->lock),
+ [serving_now_ptr] "+m" (lock->h.serving_now),
[ticket] "=&r" (tmp),
- [my_ticket] "=&r" (my_ticket));
+ [my_ticket] "=&r" (my_ticket)
+ : [inc] "r" (inc));
}
smp_llsc_mb();
@@ -136,47 +135,16 @@
static inline void arch_spin_unlock(arch_spinlock_t *lock)
{
- int tmp;
-
- smp_mb__before_llsc();
-
- if (R10000_LLSC_WAR) {
- __asm__ __volatile__ (
- " # arch_spin_unlock \n"
- "1: ll %[ticket], %[ticket_ptr] \n"
- " addiu %[ticket], %[ticket], 1 \n"
- " ori %[ticket], %[ticket], 0x2000 \n"
- " xori %[ticket], %[ticket], 0x2000 \n"
- " sc %[ticket], %[ticket_ptr] \n"
- " beqzl %[ticket], 1b \n"
- : [ticket_ptr] "+m" (lock->lock),
- [ticket] "=&r" (tmp));
- } else {
- __asm__ __volatile__ (
- " .set push # arch_spin_unlock \n"
- " .set noreorder \n"
- " \n"
- " ll %[ticket], %[ticket_ptr] \n"
- "1: addiu %[ticket], %[ticket], 1 \n"
- " ori %[ticket], %[ticket], 0x2000 \n"
- " xori %[ticket], %[ticket], 0x2000 \n"
- " sc %[ticket], %[ticket_ptr] \n"
- " beqz %[ticket], 2f \n"
- " nop \n"
- " \n"
- " .subsection 2 \n"
- "2: b 1b \n"
- " ll %[ticket], %[ticket_ptr] \n"
- " .previous \n"
- " .set pop \n"
- : [ticket_ptr] "+m" (lock->lock),
- [ticket] "=&r" (tmp));
- }
+ unsigned int serving_now = lock->h.serving_now + 1;
+ wmb();
+ lock->h.serving_now = (u16)serving_now;
+ nudge_writes();
}
static inline unsigned int arch_spin_trylock(arch_spinlock_t *lock)
{
int tmp, tmp2, tmp3;
+ int inc = 0x10000;
if (R10000_LLSC_WAR) {
__asm__ __volatile__ (
@@ -184,11 +152,11 @@
" .set noreorder \n"
" \n"
"1: ll %[ticket], %[ticket_ptr] \n"
- " srl %[my_ticket], %[ticket], 14 \n"
- " andi %[my_ticket], %[my_ticket], 0x1fff \n"
- " andi %[now_serving], %[ticket], 0x1fff \n"
+ " srl %[my_ticket], %[ticket], 16 \n"
+ " andi %[my_ticket], %[my_ticket], 0xffff \n"
+ " andi %[now_serving], %[ticket], 0xffff \n"
" bne %[my_ticket], %[now_serving], 3f \n"
- " addiu %[ticket], %[ticket], 0x4000 \n"
+ " addu %[ticket], %[ticket], %[inc] \n"
" sc %[ticket], %[ticket_ptr] \n"
" beqzl %[ticket], 1b \n"
" li %[ticket], 1 \n"
@@ -201,33 +169,33 @@
: [ticket_ptr] "+m" (lock->lock),
[ticket] "=&r" (tmp),
[my_ticket] "=&r" (tmp2),
- [now_serving] "=&r" (tmp3));
+ [now_serving] "=&r" (tmp3)
+ : [inc] "r" (inc));
} else {
__asm__ __volatile__ (
" .set push # arch_spin_trylock \n"
" .set noreorder \n"
" \n"
- " ll %[ticket], %[ticket_ptr] \n"
- "1: srl %[my_ticket], %[ticket], 14 \n"
- " andi %[my_ticket], %[my_ticket], 0x1fff \n"
- " andi %[now_serving], %[ticket], 0x1fff \n"
+ "1: ll %[ticket], %[ticket_ptr] \n"
+ " srl %[my_ticket], %[ticket], 16 \n"
+ " andi %[my_ticket], %[my_ticket], 0xffff \n"
+ " andi %[now_serving], %[ticket], 0xffff \n"
" bne %[my_ticket], %[now_serving], 3f \n"
- " addiu %[ticket], %[ticket], 0x4000 \n"
+ " addu %[ticket], %[ticket], %[inc] \n"
" sc %[ticket], %[ticket_ptr] \n"
- " beqz %[ticket], 4f \n"
+ " beqz %[ticket], 1b \n"
" li %[ticket], 1 \n"
"2: \n"
" .subsection 2 \n"
"3: b 2b \n"
" li %[ticket], 0 \n"
- "4: b 1b \n"
- " ll %[ticket], %[ticket_ptr] \n"
" .previous \n"
" .set pop \n"
: [ticket_ptr] "+m" (lock->lock),
[ticket] "=&r" (tmp),
[my_ticket] "=&r" (tmp2),
- [now_serving] "=&r" (tmp3));
+ [now_serving] "=&r" (tmp3)
+ : [inc] "r" (inc));
}
smp_llsc_mb();