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Commit 2c86963b authored by Tony Luck's avatar Tony Luck
Browse files

[IA64] implement ticket locks for Itanium 



Back in January 2008 Nick Piggin implemented "ticket" spinlocks
for X86 (See commit 314cdbef).

IA64 implementation has a couple of differences because of the
available atomic operations ... e.g. we have no fetchadd2 instruction
that operates on a 16-bit quantity so we make ticket locks use
a 32-bit word for each of the current ticket and now-serving values.

Performance on uncontended locks is about 8% worse than the previous
implementation, but this seems a good trade for determinism in the
contended case. Performance impact on macro-level benchmarks is in
the noise.

Signed-off-by: default avatarTony Luck <tony.luck@intel.com>
parent 53cddfcc

arch/ia64/Kconfig

+1 −3
Original line number Diff line number Diff line
@@ -60,9 +60,7 @@ config IOMMU_HELPER 
       bool



config GENERIC_LOCKBREAK

	bool

	default y

	depends on SMP && PREEMPT

	def_bool n



config RWSEM_XCHGADD_ALGORITHM

	bool

arch/ia64/include/asm/spinlock.h

+89 −86
Original line number Diff line number Diff line
@@ -19,103 +19,106 @@ 


#define __raw_spin_lock_init(x)			((x)->lock = 0)



#ifdef ASM_SUPPORTED

/*

 * Try to get the lock.  If we fail to get the lock, make a non-standard call to

 * ia64_spinlock_contention().  We do not use a normal call because that would force all

 * callers of __raw_spin_lock() to be non-leaf routines.  Instead, ia64_spinlock_contention() is

 * carefully coded to touch only those registers that __raw_spin_lock() marks "clobbered".

 * Ticket locks are conceptually two parts, one indicating the current head of

 * the queue, and the other indicating the current tail. The lock is acquired

 * by atomically noting the tail and incrementing it by one (thus adding

 * ourself to the queue and noting our position), then waiting until the head

 * becomes equal to the the initial value of the tail.

 *

 *   63                     32  31                      0

 *  +----------------------------------------------------+

 *  |  next_ticket_number      |     now_serving         |

 *  +----------------------------------------------------+

 */



#define IA64_SPINLOCK_CLOBBERS "ar.ccv", "ar.pfs", "p14", "p15", "r27", "r28", "r29", "r30", "b6", "memory"

#define TICKET_SHIFT	32



static inline void

__raw_spin_lock_flags (raw_spinlock_t *lock, unsigned long flags)

static __always_inline void __ticket_spin_lock(raw_spinlock_t *lock)

{

	register volatile unsigned int *ptr asm ("r31") = &lock->lock;



#if (__GNUC__ == 3 && __GNUC_MINOR__ < 3)

# ifdef CONFIG_ITANIUM

	/* don't use brl on Itanium... */

	asm volatile ("{\n\t"

		      "  mov ar.ccv = r0\n\t"

		      "  mov r28 = ip\n\t"

		      "  mov r30 = 1;;\n\t"

		      "}\n\t"

		      "cmpxchg4.acq r30 = [%1], r30, ar.ccv\n\t"

		      "movl r29 = ia64_spinlock_contention_pre3_4;;\n\t"

		      "cmp4.ne p14, p0 = r30, r0\n\t"

		      "mov b6 = r29;;\n\t"

		      "mov r27=%2\n\t"

		      "(p14) br.cond.spnt.many b6"

		      : "=r"(ptr) : "r"(ptr), "r" (flags) : IA64_SPINLOCK_CLOBBERS);

# else

	asm volatile ("{\n\t"

		      "  mov ar.ccv = r0\n\t"

		      "  mov r28 = ip\n\t"

		      "  mov r30 = 1;;\n\t"

		      "}\n\t"

		      "cmpxchg4.acq r30 = [%1], r30, ar.ccv;;\n\t"

		      "cmp4.ne p14, p0 = r30, r0\n\t"

		      "mov r27=%2\n\t"

		      "(p14) brl.cond.spnt.many ia64_spinlock_contention_pre3_4;;"

		      : "=r"(ptr) : "r"(ptr), "r" (flags) : IA64_SPINLOCK_CLOBBERS);

# endif /* CONFIG_MCKINLEY */

#else

# ifdef CONFIG_ITANIUM

	/* don't use brl on Itanium... */

	/* mis-declare, so we get the entry-point, not it's function descriptor: */

	asm volatile ("mov r30 = 1\n\t"

		      "mov r27=%2\n\t"

		      "mov ar.ccv = r0;;\n\t"

		      "cmpxchg4.acq r30 = [%0], r30, ar.ccv\n\t"

		      "movl r29 = ia64_spinlock_contention;;\n\t"

		      "cmp4.ne p14, p0 = r30, r0\n\t"

		      "mov b6 = r29;;\n\t"

		      "(p14) br.call.spnt.many b6 = b6"

		      : "=r"(ptr) : "r"(ptr), "r" (flags) : IA64_SPINLOCK_CLOBBERS);

# else

	asm volatile ("mov r30 = 1\n\t"

		      "mov r27=%2\n\t"

		      "mov ar.ccv = r0;;\n\t"

		      "cmpxchg4.acq r30 = [%0], r30, ar.ccv;;\n\t"

		      "cmp4.ne p14, p0 = r30, r0\n\t"

		      "(p14) brl.call.spnt.many b6=ia64_spinlock_contention;;"

		      : "=r"(ptr) : "r"(ptr), "r" (flags) : IA64_SPINLOCK_CLOBBERS);

# endif /* CONFIG_MCKINLEY */

#endif

	int	*p = (int *)&lock->lock, turn, now_serving;



	now_serving = *p;

	turn = ia64_fetchadd(1, p+1, acq);



	if (turn == now_serving)

		return;



	do {

		cpu_relax();

	} while (ACCESS_ONCE(*p) != turn);

}



#define __raw_spin_lock(lock) __raw_spin_lock_flags(lock, 0)

static __always_inline int __ticket_spin_trylock(raw_spinlock_t *lock)

{

	long tmp = ACCESS_ONCE(lock->lock), try;



	if (!(((tmp >> TICKET_SHIFT) ^ tmp) & ((1L << TICKET_SHIFT) - 1))) {

		try = tmp + (1L << TICKET_SHIFT);



/* Unlock by doing an ordered store and releasing the cacheline with nta */

static inline void __raw_spin_unlock(raw_spinlock_t *x) {

	barrier();

	asm volatile ("st4.rel.nta [%0] = r0\n\t" :: "r"(x));

		return ia64_cmpxchg(acq, &lock->lock, tmp, try, sizeof (tmp)) == tmp;

	}

	return 0;

}



#else /* !ASM_SUPPORTED */

#define __raw_spin_lock_flags(lock, flags) __raw_spin_lock(lock)

# define __raw_spin_lock(x)								\

do {											\

	__u32 *ia64_spinlock_ptr = (__u32 *) (x);					\

	__u64 ia64_spinlock_val;							\

	ia64_spinlock_val = ia64_cmpxchg4_acq(ia64_spinlock_ptr, 1, 0);			\

	if (unlikely(ia64_spinlock_val)) {						\

		do {									\

			while (*ia64_spinlock_ptr)					\

				ia64_barrier();						\

			ia64_spinlock_val = ia64_cmpxchg4_acq(ia64_spinlock_ptr, 1, 0);	\

		} while (ia64_spinlock_val);						\

	}										\

} while (0)

#define __raw_spin_unlock(x)	do { barrier(); ((raw_spinlock_t *) x)->lock = 0; } while (0)

#endif /* !ASM_SUPPORTED */

static __always_inline void __ticket_spin_unlock(raw_spinlock_t *lock)

{

	int	*p = (int *)&lock->lock;



	(void)ia64_fetchadd(1, p, rel);

}



static inline int __ticket_spin_is_locked(raw_spinlock_t *lock)

{

	long tmp = ACCESS_ONCE(lock->lock);



#define __raw_spin_is_locked(x)		((x)->lock != 0)

#define __raw_spin_trylock(x)		(cmpxchg_acq(&(x)->lock, 0, 1) == 0)

#define __raw_spin_unlock_wait(lock) \

	do { while (__raw_spin_is_locked(lock)) cpu_relax(); } while (0)

	return !!(((tmp >> TICKET_SHIFT) ^ tmp) & ((1L << TICKET_SHIFT) - 1));

}



static inline int __ticket_spin_is_contended(raw_spinlock_t *lock)

{

	long tmp = ACCESS_ONCE(lock->lock);



	return (((tmp >> TICKET_SHIFT) - tmp) & ((1L << TICKET_SHIFT) - 1)) > 1;

}



static inline int __raw_spin_is_locked(raw_spinlock_t *lock)

{

	return __ticket_spin_is_locked(lock);

}



static inline int __raw_spin_is_contended(raw_spinlock_t *lock)

{

	return __ticket_spin_is_contended(lock);

}

#define __raw_spin_is_contended	__raw_spin_is_contended



static __always_inline void __raw_spin_lock(raw_spinlock_t *lock)

{

	__ticket_spin_lock(lock);

}



static __always_inline int __raw_spin_trylock(raw_spinlock_t *lock)

{

	return __ticket_spin_trylock(lock);

}



static __always_inline void __raw_spin_unlock(raw_spinlock_t *lock)

{

	__ticket_spin_unlock(lock);

}



static __always_inline void __raw_spin_lock_flags(raw_spinlock_t *lock,

						  unsigned long flags)

{

	__raw_spin_lock(lock);

}



static inline void __raw_spin_unlock_wait(raw_spinlock_t *lock)

{

	while (__raw_spin_is_locked(lock))

		cpu_relax();

}



#define __raw_read_can_lock(rw)		(*(volatile int *)(rw) >= 0)

#define __raw_write_can_lock(rw)	(*(volatile int *)(rw) == 0)

arch/ia64/include/asm/spinlock_types.h

+1 −1
Original line number Diff line number Diff line
@@ -6,7 +6,7 @@ 
#endif



typedef struct {

	volatile unsigned int lock;

	volatile unsigned long lock;

} raw_spinlock_t;



#define __RAW_SPIN_LOCK_UNLOCKED	{ 0 }

arch/ia64/kernel/head.S

+0 −89
Original line number Diff line number Diff line
@@ -1130,95 +1130,6 @@ SET_REG(b5); 
#endif /* CONFIG_IA64_BRL_EMU */



#ifdef CONFIG_SMP

	/*

	 * This routine handles spinlock contention.  It uses a non-standard calling

	 * convention to avoid converting leaf routines into interior routines.  Because

	 * of this special convention, there are several restrictions:

	 *

	 * - do not use gp relative variables, this code is called from the kernel

	 *   and from modules, r1 is undefined.

	 * - do not use stacked registers, the caller owns them.

	 * - do not use the scratch stack space, the caller owns it.

	 * - do not use any registers other than the ones listed below

	 *

	 * Inputs:

	 *   ar.pfs - saved CFM of caller

	 *   ar.ccv - 0 (and available for use)

	 *   r27    - flags from spin_lock_irqsave or 0.  Must be preserved.

	 *   r28    - available for use.

	 *   r29    - available for use.

	 *   r30    - available for use.

	 *   r31    - address of lock, available for use.

	 *   b6     - return address

	 *   p14    - available for use.

	 *   p15    - used to track flag status.

	 *

	 * If you patch this code to use more registers, do not forget to update

	 * the clobber lists for spin_lock() in arch/ia64/include/asm/spinlock.h.

	 */



#if (__GNUC__ == 3 && __GNUC_MINOR__ < 3)



GLOBAL_ENTRY(ia64_spinlock_contention_pre3_4)

	.prologue

	.save ar.pfs, r0	// this code effectively has a zero frame size

	.save rp, r28

	.body

	nop 0

	tbit.nz p15,p0=r27,IA64_PSR_I_BIT

	.restore sp		// pop existing prologue after next insn

	mov b6 = r28

	.prologue

	.save ar.pfs, r0

	.altrp b6

	.body

	;;

(p15)	ssm psr.i		// reenable interrupts if they were on

				// DavidM says that srlz.d is slow and is not required in this case

.wait:

	// exponential backoff, kdb, lockmeter etc. go in here

	hint @pause

	ld4 r30=[r31]		// don't use ld4.bias; if it's contended, we won't write the word

	nop 0

	;;

	cmp4.ne p14,p0=r30,r0

(p14)	br.cond.sptk.few .wait

(p15)	rsm psr.i		// disable interrupts if we reenabled them

	br.cond.sptk.few b6	// lock is now free, try to acquire

	.global ia64_spinlock_contention_pre3_4_end	// for kernprof

ia64_spinlock_contention_pre3_4_end:

END(ia64_spinlock_contention_pre3_4)



#else



GLOBAL_ENTRY(ia64_spinlock_contention)

	.prologue

	.altrp b6

	.body

	tbit.nz p15,p0=r27,IA64_PSR_I_BIT

	;;

.wait:

(p15)	ssm psr.i		// reenable interrupts if they were on

				// DavidM says that srlz.d is slow and is not required in this case

.wait2:

	// exponential backoff, kdb, lockmeter etc. go in here

	hint @pause

	ld4 r30=[r31]		// don't use ld4.bias; if it's contended, we won't write the word

	;;

	cmp4.ne p14,p0=r30,r0

	mov r30 = 1

(p14)	br.cond.sptk.few .wait2

(p15)	rsm psr.i		// disable interrupts if we reenabled them

	;;

	cmpxchg4.acq r30=[r31], r30, ar.ccv

	;;

	cmp4.ne p14,p0=r0,r30

(p14)	br.cond.sptk.few .wait



	br.ret.sptk.many b6	// lock is now taken

END(ia64_spinlock_contention)



#endif



#ifdef CONFIG_HOTPLUG_CPU

GLOBAL_ENTRY(ia64_jump_to_sal)

arch/ia64/kernel/ia64_ksyms.c

+0 −20
Original line number Diff line number Diff line
@@ -84,26 +84,6 @@ EXPORT_SYMBOL(ia64_save_scratch_fpregs); 
#include <asm/unwind.h>

EXPORT_SYMBOL(unw_init_running);



#ifdef ASM_SUPPORTED

# ifdef CONFIG_SMP

#  if (__GNUC__ == 3 && __GNUC_MINOR__ < 3)

/*

 * This is not a normal routine and we don't want a function descriptor for it, so we use

 * a fake declaration here.

 */

extern char ia64_spinlock_contention_pre3_4;

EXPORT_SYMBOL(ia64_spinlock_contention_pre3_4);

#  else

/*

 * This is not a normal routine and we don't want a function descriptor for it, so we use

 * a fake declaration here.

 */

extern char ia64_spinlock_contention;

EXPORT_SYMBOL(ia64_spinlock_contention);

#  endif

# endif

#endif



#if defined(CONFIG_IA64_ESI) || defined(CONFIG_IA64_ESI_MODULE)

extern void esi_call_phys (void);

EXPORT_SYMBOL_GPL(esi_call_phys);