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Commit 7f7e6e28 authored by Martin Schwidefsky's avatar Martin Schwidefsky
Browse files

s390/spinlock: add niai spinlock hints 



The z14 machine introduces new mode of the next-instruction-access-intent
NIAI instruction. With NIAI-8 it is possible to pin a cache-line on a
CPU for a small amount of time, NIAI-7 releases the cache-line again.
Finally NIAI-4 can be used to prevent the CPU to speculatively access
memory beyond the compare-and-swap instruction to get the lock.

Use these instruction in the spinlock code.

Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
parent 8351378f

arch/s390/include/asm/spinlock.h

+5 −4
Original line number Diff line number Diff line
@@ -92,10 +92,11 @@ static inline void arch_spin_unlock(arch_spinlock_t *lp) 
{

	typecheck(int, lp->lock);

	asm volatile(

#ifdef CONFIG_HAVE_MARCH_ZEC12_FEATURES

		"	.long	0xb2fa0070\n"	/* NIAI 7 */

#endif

		"	st	%1,%0\n"

		: "+Q" (lp->lock)

		: "d" (0)

		: "cc", "memory");

		: "=Q" (lp->lock) : "d" (0) : "cc", "memory");

}



static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)

arch/s390/lib/spinlock.c

+51 −36
Original line number Diff line number Diff line
@@ -32,42 +32,63 @@ static int __init spin_retry_setup(char *str) 
}

__setup("spin_retry=", spin_retry_setup);



static inline int arch_load_niai4(int *lock)

{

	int owner;



	asm volatile(

#ifdef CONFIG_HAVE_MARCH_ZEC12_FEATURES

		"	.long	0xb2fa0040\n"	/* NIAI 4 */

#endif

		"	l	%0,%1\n"

		: "=d" (owner) : "Q" (*lock) : "memory");

       return owner;

}



static inline int arch_cmpxchg_niai8(int *lock, int old, int new)

{

	int expected = old;



	asm volatile(

#ifdef CONFIG_HAVE_MARCH_ZEC12_FEATURES

		"	.long	0xb2fa0080\n"	/* NIAI 8 */

#endif

		"	cs	%0,%3,%1\n"

		: "=d" (old), "=Q" (*lock)

		: "0" (old), "d" (new), "Q" (*lock)

		: "cc", "memory");

	return expected == old;

}



void arch_spin_lock_wait(arch_spinlock_t *lp)

{

	int cpu = SPINLOCK_LOCKVAL;

	int owner, count, first_diag;

	int owner, count;



	/* Pass the virtual CPU to the lock holder if it is not running */

	owner = arch_load_niai4(&lp->lock);

	if (owner && arch_vcpu_is_preempted(~owner))

		smp_yield_cpu(~owner);



	first_diag = 1;

	count = spin_retry;

	while (1) {

		owner = ACCESS_ONCE(lp->lock);

		owner = arch_load_niai4(&lp->lock);

		/* Try to get the lock if it is free. */

		if (!owner) {

			if (__atomic_cmpxchg_bool(&lp->lock, 0, cpu))

			if (arch_cmpxchg_niai8(&lp->lock, 0, cpu))

				return;

			continue;

		}

		/* First iteration: check if the lock owner is running. */

		if (first_diag && arch_vcpu_is_preempted(~owner)) {

			smp_yield_cpu(~owner);

			first_diag = 0;

		if (count-- >= 0)

			continue;

		}

		/* Loop for a while on the lock value. */

		count = spin_retry;

		do {

			owner = ACCESS_ONCE(lp->lock);

		} while (owner && count-- > 0);

		if (!owner)

			continue;

		/*

		 * For multiple layers of hypervisors, e.g. z/VM + LPAR

		 * yield the CPU unconditionally. For LPAR rely on the

		 * sense running status.

		 */

		if (!MACHINE_IS_LPAR || arch_vcpu_is_preempted(~owner)) {

		if (!MACHINE_IS_LPAR || arch_vcpu_is_preempted(~owner))

			smp_yield_cpu(~owner);

			first_diag = 0;

		}

	}

}

EXPORT_SYMBOL(arch_spin_lock_wait);
@@ -75,42 +96,36 @@ EXPORT_SYMBOL(arch_spin_lock_wait); 
void arch_spin_lock_wait_flags(arch_spinlock_t *lp, unsigned long flags)

{

	int cpu = SPINLOCK_LOCKVAL;

	int owner, count, first_diag;

	int owner, count;



	local_irq_restore(flags);

	first_diag = 1;



	/* Pass the virtual CPU to the lock holder if it is not running */

	owner = arch_load_niai4(&lp->lock);

	if (owner && arch_vcpu_is_preempted(~owner))

		smp_yield_cpu(~owner);



	count = spin_retry;

	while (1) {

		owner = ACCESS_ONCE(lp->lock);

		owner = arch_load_niai4(&lp->lock);

		/* Try to get the lock if it is free. */

		if (!owner) {

			local_irq_disable();

			if (__atomic_cmpxchg_bool(&lp->lock, 0, cpu))

			if (arch_cmpxchg_niai8(&lp->lock, 0, cpu))

				return;

			local_irq_restore(flags);

			continue;

		}

		/* Check if the lock owner is running. */

		if (first_diag && arch_vcpu_is_preempted(~owner)) {

			smp_yield_cpu(~owner);

			first_diag = 0;

		if (count-- >= 0)

			continue;

		}

		/* Loop for a while on the lock value. */

		count = spin_retry;

		do {

			owner = ACCESS_ONCE(lp->lock);

		} while (owner && count-- > 0);

		if (!owner)

			continue;

		/*

		 * For multiple layers of hypervisors, e.g. z/VM + LPAR

		 * yield the CPU unconditionally. For LPAR rely on the

		 * sense running status.

		 */

		if (!MACHINE_IS_LPAR || arch_vcpu_is_preempted(~owner)) {

		if (!MACHINE_IS_LPAR || arch_vcpu_is_preempted(~owner))

			smp_yield_cpu(~owner);

			first_diag = 0;

		}

	}

}

EXPORT_SYMBOL(arch_spin_lock_wait_flags);