Commit 500c2e1f authored by David Daney's avatar David Daney Committed by Ralf Baechle
Browse files

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: default avatarDavid Daney <ddaney@caviumnetworks.com>
To: linux-mips@linux-mips.org
Patchwork: http://patchwork.linux-mips.org/patch/937/


Signed-off-by: default avatarRalf Baechle <ralf@linux-mips.org>
parent e275ed5e

arch/mips/include/asm/barrier.h

+6 −0
Original line number Diff line number Diff line
@@ -168,8 +168,14 @@ 


#ifdef CONFIG_CPU_CAVIUM_OCTEON

#define smp_mb__before_llsc() smp_wmb()

/* Cause previous writes to become visible on all CPUs as soon as possible */

#define nudge_writes() __asm__ __volatile__(".set push\n\t"		\

					    ".set arch=octeon\n\t"	\

					    "syncw\n\t"			\

					    ".set pop" : : : "memory")

#else

#define smp_mb__before_llsc() smp_llsc_mb()

#define nudge_writes() mb()

#endif



#endif /* __ASM_BARRIER_H */

arch/mips/include/asm/spinlock.h

+43 −75
Original line number Diff line number Diff line
@@ -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_locked(arch_spinlock_t *lock) 


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 @@ static inline void arch_spin_lock(arch_spinlock_t *lock) 
{

	int my_ticket;

	int tmp;

	int inc = 0x10000;



	if (R10000_LLSC_WAR) {

		__asm__ __volatile__ (
@@ -64,25 +65,24 @@ static inline void arch_spin_lock(arch_spinlock_t *lock) 
		"	.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 @@ static inline void arch_spin_lock(arch_spinlock_t *lock) 
		"	.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 @@ static inline void arch_spin_lock(arch_spinlock_t *lock) 
		"	.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_lock(arch_spinlock_t *lock) 


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 @@ static inline unsigned int arch_spin_trylock(arch_spinlock_t *lock) 
		"	.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 @@ static inline unsigned int arch_spin_trylock(arch_spinlock_t *lock) 
		: [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();

arch/mips/include/asm/spinlock_types.h

+18 −6
Original line number Diff line number Diff line
@@ -5,16 +5,28 @@ 
# error "please don't include this file directly"

#endif



typedef struct {

#include <linux/types.h>



#include <asm/byteorder.h>



typedef union {

	/*

	 * bits  0..13: serving_now

	 * bits 14    : junk data

	 * bits 15..28: ticket

	 * bits  0..15 : serving_now

	 * bits 16..31 : ticket

	 */

	unsigned int lock;

	u32 lock;

	struct {

#ifdef __BIG_ENDIAN

		u16 ticket;

		u16 serving_now;

#else

		u16 serving_now;

		u16 ticket;

#endif

	} h;

} arch_spinlock_t;



#define __ARCH_SPIN_LOCK_UNLOCKED	{ 0 }

#define __ARCH_SPIN_LOCK_UNLOCKED	{ .lock = 0 }



typedef struct {

	volatile unsigned int lock;

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