s390/rwlock: improve writer fairness

[mirror_ubuntu-jammy-kernel.git] / arch / s390 / lib / spinlock.c

/*
 *    Out of line spinlock code.
 *
 *    Copyright IBM Corp. 2004, 2006
 *    Author(s): Martin Schwidefsky (schwidefsky@de.ibm.com)
 */

#include <linux/types.h>
#include <linux/module.h>
#include <linux/spinlock.h>
#include <linux/init.h>
#include <linux/smp.h>
#include <asm/io.h>

int spin_retry = 1000;

/**
 * spin_retry= parameter
 */
static int __init spin_retry_setup(char *str)
{
	spin_retry = simple_strtoul(str, &str, 0);
	return 1;
}
__setup("spin_retry=", spin_retry_setup);

void arch_spin_lock_wait(arch_spinlock_t *lp)
{
	unsigned int cpu = SPINLOCK_LOCKVAL;
	unsigned int owner;
	int count;

	while (1) {
		owner = ACCESS_ONCE(lp->lock);
		/* Try to get the lock if it is free. */
		if (!owner) {
			if (_raw_compare_and_swap(&lp->lock, 0, cpu))
				return;
			continue;
		}
		/* Check if the lock owner is running. */
		if (!smp_vcpu_scheduled(~owner)) {
			smp_yield_cpu(~owner);
			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 if the lock is still unavailable.
		 */
		if (!MACHINE_IS_LPAR)
			smp_yield_cpu(~owner);
	}
}
EXPORT_SYMBOL(arch_spin_lock_wait);

void arch_spin_lock_wait_flags(arch_spinlock_t *lp, unsigned long flags)
{
	unsigned int cpu = SPINLOCK_LOCKVAL;
	unsigned int owner;
	int count;

	local_irq_restore(flags);
	while (1) {
		owner = ACCESS_ONCE(lp->lock);
		/* Try to get the lock if it is free. */
		if (!owner) {
			local_irq_disable();
			if (_raw_compare_and_swap(&lp->lock, 0, cpu))
				return;
			local_irq_restore(flags);
		}
		/* Check if the lock owner is running. */
		if (!smp_vcpu_scheduled(~owner)) {
			smp_yield_cpu(~owner);
			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 if the lock is still unavailable.
		 */
		if (!MACHINE_IS_LPAR)
			smp_yield_cpu(~owner);
	}
}
EXPORT_SYMBOL(arch_spin_lock_wait_flags);

int arch_spin_trylock_retry(arch_spinlock_t *lp)
{
	int count;

	for (count = spin_retry; count > 0; count--)
		if (arch_spin_trylock_once(lp))
			return 1;
	return 0;
}
EXPORT_SYMBOL(arch_spin_trylock_retry);

void _raw_read_lock_wait(arch_rwlock_t *rw)
{
	unsigned int owner, old;
	int count = spin_retry;

	owner = 0;
	while (1) {
		if (count-- <= 0) {
			if (owner && !smp_vcpu_scheduled(~owner))
				smp_yield_cpu(~owner);
			count = spin_retry;
		}
		old = ACCESS_ONCE(rw->lock);
		owner = ACCESS_ONCE(rw->owner);
		if ((int) old < 0)
			continue;
		if (_raw_compare_and_swap(&rw->lock, old, old + 1))
			return;
	}
}
EXPORT_SYMBOL(_raw_read_lock_wait);

int _raw_read_trylock_retry(arch_rwlock_t *rw)
{
	unsigned int old;
	int count = spin_retry;

	while (count-- > 0) {
		old = ACCESS_ONCE(rw->lock);
		if ((int) old < 0)
			continue;
		if (_raw_compare_and_swap(&rw->lock, old, old + 1))
			return 1;
	}
	return 0;
}
EXPORT_SYMBOL(_raw_read_trylock_retry);

void _raw_write_lock_wait(arch_rwlock_t *rw)
{
	unsigned int owner, old, prev;
	int count = spin_retry;

	prev = 0x80000000;
	owner = 0;
	while (1) {
		if (count-- <= 0) {
			if (owner && !smp_vcpu_scheduled(~owner))
				smp_yield_cpu(~owner);
			count = spin_retry;
		}
		old = ACCESS_ONCE(rw->lock);
		owner = ACCESS_ONCE(rw->owner);
		if ((int) old >= 0 &&
		    _raw_compare_and_swap(&rw->lock, old, old | 0x80000000))
			prev = old;
		else
			smp_rmb();
		if ((old & 0x7fffffff) == 0 && (int) prev >= 0)
			break;
	}
}
EXPORT_SYMBOL(_raw_write_lock_wait);

int _raw_write_trylock_retry(arch_rwlock_t *rw)
{
	unsigned int old;
	int count = spin_retry;

	while (count-- > 0) {
		old = ACCESS_ONCE(rw->lock);
		if (old)
			continue;
		if (_raw_compare_and_swap(&rw->lock, 0, 0x80000000))
			return 1;
	}
	return 0;
}
EXPORT_SYMBOL(_raw_write_trylock_retry);

void arch_lock_relax(unsigned int cpu)
{
	if (!cpu)
		return;
	if (MACHINE_IS_LPAR && smp_vcpu_scheduled(~cpu))
		return;
	smp_yield_cpu(~cpu);
}
EXPORT_SYMBOL(arch_lock_relax);