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Commit 2c72a44e authored by Martin Schwidefsky's avatar Martin Schwidefsky
Browse files

s390/spinlock: add compare-and-delay to lock wait loops 



Add the compare-and-delay instruction to the spin-lock and rw-lock
retry loops. A CPU executing the compare-and-delay instruction stops
until the lock value has changed. This is done to make the locking
code for contended locks to behave better in regard to the multi-
hreading facility. A thread of a core executing a compare-and-delay
will allow the other threads of a core to get a larger share of the
core resources.

Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
parent 55b5eb75

arch/s390/include/asm/setup.h

+3 −0
Original line number Diff line number Diff line
@@ -57,6 +57,7 @@ extern void detect_memory_memblock(void); 
#define MACHINE_FLAG_TE		(1UL << 15)

#define MACHINE_FLAG_TLB_LC	(1UL << 17)

#define MACHINE_FLAG_VX		(1UL << 18)

#define MACHINE_FLAG_CAD	(1UL << 19)



#define MACHINE_IS_VM		(S390_lowcore.machine_flags & MACHINE_FLAG_VM)

#define MACHINE_IS_KVM		(S390_lowcore.machine_flags & MACHINE_FLAG_KVM)
@@ -80,6 +81,7 @@ extern void detect_memory_memblock(void); 
#define MACHINE_HAS_TE		(0)

#define MACHINE_HAS_TLB_LC	(0)

#define MACHINE_HAS_VX		(0)

#define MACHINE_HAS_CAD		(0)

#else /* CONFIG_64BIT */

#define MACHINE_HAS_IEEE	(1)

#define MACHINE_HAS_CSP		(1)
@@ -93,6 +95,7 @@ extern void detect_memory_memblock(void); 
#define MACHINE_HAS_TE		(S390_lowcore.machine_flags & MACHINE_FLAG_TE)

#define MACHINE_HAS_TLB_LC	(S390_lowcore.machine_flags & MACHINE_FLAG_TLB_LC)

#define MACHINE_HAS_VX		(S390_lowcore.machine_flags & MACHINE_FLAG_VX)

#define MACHINE_HAS_CAD		(S390_lowcore.machine_flags & MACHINE_FLAG_CAD)

#endif /* CONFIG_64BIT */



/*

arch/s390/kernel/early.c

+18 −0
Original line number Diff line number Diff line
@@ -393,9 +393,27 @@ static __init void detect_machine_facilities(void) 
		S390_lowcore.machine_flags |= MACHINE_FLAG_TLB_LC;

	if (test_facility(129))

		S390_lowcore.machine_flags |= MACHINE_FLAG_VX;

	if (test_facility(128))

		S390_lowcore.machine_flags |= MACHINE_FLAG_CAD;

#endif

}



static int __init nocad_setup(char *str)

{

	S390_lowcore.machine_flags &= ~MACHINE_FLAG_CAD;

	return 0;

}

early_param("nocad", nocad_setup);



static int __init cad_init(void)

{

	if (MACHINE_HAS_CAD)

		/* Enable problem state CAD. */

		__ctl_set_bit(2, 3);

	return 0;

}

early_initcall(cad_init);



static __init void rescue_initrd(void)

{

#ifdef CONFIG_BLK_DEV_INITRD

arch/s390/lib/spinlock.c

+45 −7
Original line number Diff line number Diff line
@@ -12,7 +12,15 @@ 
#include <linux/smp.h>

#include <asm/io.h>



int spin_retry = 1000;

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
@@ -24,6 +32,11 @@ static int __init spin_retry_setup(char *str) 
}

__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));

}



void arch_spin_lock_wait(arch_spinlock_t *lp)

{

	unsigned int cpu = SPINLOCK_LOCKVAL;
@@ -46,6 +59,8 @@ void arch_spin_lock_wait(arch_spinlock_t *lp) 
		/* 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)
@@ -84,6 +99,8 @@ void arch_spin_lock_wait_flags(arch_spinlock_t *lp, unsigned long flags) 
		/* 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)
@@ -100,11 +117,19 @@ 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--)

		if (arch_spin_trylock_once(lp))

	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);
@@ -126,8 +151,11 @@ void _raw_read_lock_wait(arch_rwlock_t *rw) 
		}

		old = ACCESS_ONCE(rw->lock);

		owner = ACCESS_ONCE(rw->owner);

		if ((int) old < 0)

		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;

	}
@@ -141,8 +169,11 @@ int _raw_read_trylock_retry(arch_rwlock_t *rw) 


	while (count-- > 0) {

		old = ACCESS_ONCE(rw->lock);

		if ((int) old < 0)

		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;

	}
@@ -173,6 +204,8 @@ void _raw_write_lock_wait(arch_rwlock_t *rw, unsigned int 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);
@@ -201,6 +234,8 @@ void _raw_write_lock_wait(arch_rwlock_t *rw) 
			smp_rmb();

		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);
@@ -214,8 +249,11 @@ int _raw_write_trylock_retry(arch_rwlock_t *rw) 


	while (count-- > 0) {

		old = ACCESS_ONCE(rw->lock);

		if (old)

		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;

	}