linux/arch/s390/lib/spinlock.c
Martin Schwidefsky 419123f900 s390/spinlock: do not yield to a CPU in udelay/mdelay
It does not make sense to try to relinquish the time slice with diag 0x9c
to a CPU in a state that does not allow to schedule the CPU. The scenario
where this can happen is a CPU waiting in udelay/mdelay while holding a
spin-lock.

Add a CIF bit to tag a CPU in enabled wait and use it to detect that the
yield of a CPU will not be successful and skip the diagnose call.

Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
2015-11-27 09:24:18 +01:00

292 lines
6.3 KiB
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 = -1;
static int __init spin_retry_init(void)
{
if (spin_retry < 0)
spin_retry = MACHINE_HAS_CAD ? 10 : 1000;
return 0;
}
early_initcall(spin_retry_init);
/**
* 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);
static inline void _raw_compare_and_delay(unsigned int *lock, unsigned int old)
{
asm(".insn rsy,0xeb0000000022,%0,0,%1" : : "d" (old), "Q" (*lock));
}
static inline int cpu_is_preempted(int cpu)
{
if (test_cpu_flag_of(CIF_ENABLED_WAIT, cpu))
return 0;
if (smp_vcpu_scheduled(cpu))
return 0;
return 1;
}
void arch_spin_lock_wait(arch_spinlock_t *lp)
{
unsigned int cpu = SPINLOCK_LOCKVAL;
unsigned int owner;
int count, first_diag;
first_diag = 1;
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;
}
/* First iteration: check if the lock owner is running. */
if (first_diag && cpu_is_preempted(~owner)) {
smp_yield_cpu(~owner);
first_diag = 0;
continue;
}
/* Loop for a while on the lock value. */
count = spin_retry;
do {
if (MACHINE_HAS_CAD)
_raw_compare_and_delay(&lp->lock, owner);
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 || cpu_is_preempted(~owner)) {
smp_yield_cpu(~owner);
first_diag = 0;
}
}
}
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, first_diag;
local_irq_restore(flags);
first_diag = 1;
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 (first_diag && cpu_is_preempted(~owner)) {
smp_yield_cpu(~owner);
first_diag = 0;
continue;
}
/* Loop for a while on the lock value. */
count = spin_retry;
do {
if (MACHINE_HAS_CAD)
_raw_compare_and_delay(&lp->lock, owner);
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 || cpu_is_preempted(~owner)) {
smp_yield_cpu(~owner);
first_diag = 0;
}
}
}
EXPORT_SYMBOL(arch_spin_lock_wait_flags);
int arch_spin_trylock_retry(arch_spinlock_t *lp)
{
unsigned int cpu = SPINLOCK_LOCKVAL;
unsigned int owner;
int count;
for (count = spin_retry; count > 0; count--) {
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 1;
} else if (MACHINE_HAS_CAD)
_raw_compare_and_delay(&lp->lock, owner);
}
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;
#ifdef CONFIG_HAVE_MARCH_Z196_FEATURES
__RAW_LOCK(&rw->lock, -1, __RAW_OP_ADD);
#endif
owner = 0;
while (1) {
if (count-- <= 0) {
if (owner && cpu_is_preempted(~owner))
smp_yield_cpu(~owner);
count = spin_retry;
}
old = ACCESS_ONCE(rw->lock);
owner = ACCESS_ONCE(rw->owner);
if ((int) old < 0) {
if (MACHINE_HAS_CAD)
_raw_compare_and_delay(&rw->lock, old);
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) {
if (MACHINE_HAS_CAD)
_raw_compare_and_delay(&rw->lock, old);
continue;
}
if (_raw_compare_and_swap(&rw->lock, old, old + 1))
return 1;
}
return 0;
}
EXPORT_SYMBOL(_raw_read_trylock_retry);
#ifdef CONFIG_HAVE_MARCH_Z196_FEATURES
void _raw_write_lock_wait(arch_rwlock_t *rw, unsigned int prev)
{
unsigned int owner, old;
int count = spin_retry;
owner = 0;
while (1) {
if (count-- <= 0) {
if (owner && cpu_is_preempted(~owner))
smp_yield_cpu(~owner);
count = spin_retry;
}
old = ACCESS_ONCE(rw->lock);
owner = ACCESS_ONCE(rw->owner);
smp_mb();
if ((int) old >= 0) {
prev = __RAW_LOCK(&rw->lock, 0x80000000, __RAW_OP_OR);
old = prev;
}
if ((old & 0x7fffffff) == 0 && (int) prev >= 0)
break;
if (MACHINE_HAS_CAD)
_raw_compare_and_delay(&rw->lock, old);
}
}
EXPORT_SYMBOL(_raw_write_lock_wait);
#else /* CONFIG_HAVE_MARCH_Z196_FEATURES */
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 && cpu_is_preempted(~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_mb();
if ((old & 0x7fffffff) == 0 && (int) prev >= 0)
break;
if (MACHINE_HAS_CAD)
_raw_compare_and_delay(&rw->lock, old);
}
}
EXPORT_SYMBOL(_raw_write_lock_wait);
#endif /* CONFIG_HAVE_MARCH_Z196_FEATURES */
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) {
if (MACHINE_HAS_CAD)
_raw_compare_and_delay(&rw->lock, 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 && !cpu_is_preempted(~cpu))
return;
smp_yield_cpu(~cpu);
}
EXPORT_SYMBOL(arch_lock_relax);