Commit 03a679a1 authored by Arnd Bergmann's avatar Arnd Bergmann
Browse files

Merge tag 'generic-ticket-spinlocks-v6' of... 

Merge tag 'generic-ticket-spinlocks-v6' of git://git.kernel.org/pub/scm/linux/kernel/git/palmer/linux into asm-generic

asm-generic: New generic ticket-based spinlock

This contains a new ticket-based spinlock that uses only generic
atomics and doesn't require as much from the memory system as qspinlock
does in order to be fair.  It also includes a bit of documentation about
the qspinlock and qrwlock fairness requirements.

This will soon be used by a handful of architectures that don't meet the
qspinlock requirements.

* tag 'generic-ticket-spinlocks-v6' of git://git.kernel.org/pub/scm/linux/kernel/git/palmer/linux:
  csky: Move to generic ticket-spinlock
  RISC-V: Move to queued RW locks
  RISC-V: Move to generic spinlocks
  openrisc: Move to ticket-spinlock
  asm-generic: qrwlock: Document the spinlock fairness requirements
  asm-generic: qspinlock: Indicate the use of mixed-size atomics
  asm-generic: ticket-lock: New generic ticket-based spinlock
parents fba2689e 9282d099

arch/csky/include/asm/Kbuild

+3 −0
Original line number Diff line number Diff line
@@ -3,7 +3,10 @@ generic-y += asm-offsets.h 
generic-y += extable.h

generic-y += gpio.h

generic-y += kvm_para.h

generic-y += spinlock.h

generic-y += spinlock_types.h

generic-y += qrwlock.h

generic-y += qrwlock_types.h

generic-y += parport.h

generic-y += user.h

generic-y += vmlinux.lds.h

arch/csky/include/asm/spinlock.h

deleted100644 → 0
+0 −89
Original line number Diff line number Diff line 
/* SPDX-License-Identifier: GPL-2.0 */



#ifndef __ASM_CSKY_SPINLOCK_H

#define __ASM_CSKY_SPINLOCK_H



#include <linux/spinlock_types.h>

#include <asm/barrier.h>



/*

 * Ticket-based spin-locking.

 */

static inline void arch_spin_lock(arch_spinlock_t *lock)

{

	arch_spinlock_t lockval;

	u32 ticket_next = 1 << TICKET_NEXT;

	u32 *p = &lock->lock;

	u32 tmp;



	asm volatile (

		"1:	ldex.w		%0, (%2) \n"

		"	mov		%1, %0	 \n"

		"	add		%0, %3	 \n"

		"	stex.w		%0, (%2) \n"

		"	bez		%0, 1b   \n"

		: "=&r" (tmp), "=&r" (lockval)

		: "r"(p), "r"(ticket_next)

		: "cc");



	while (lockval.tickets.next != lockval.tickets.owner)

		lockval.tickets.owner = READ_ONCE(lock->tickets.owner);



	smp_mb();

}



static inline int arch_spin_trylock(arch_spinlock_t *lock)

{

	u32 tmp, contended, res;

	u32 ticket_next = 1 << TICKET_NEXT;

	u32 *p = &lock->lock;



	do {

		asm volatile (

		"	ldex.w		%0, (%3)   \n"

		"	movi		%2, 1	   \n"

		"	rotli		%1, %0, 16 \n"

		"	cmpne		%1, %0     \n"

		"	bt		1f         \n"

		"	movi		%2, 0	   \n"

		"	add		%0, %0, %4 \n"

		"	stex.w		%0, (%3)   \n"

		"1:				   \n"

		: "=&r" (res), "=&r" (tmp), "=&r" (contended)

		: "r"(p), "r"(ticket_next)

		: "cc");

	} while (!res);



	if (!contended)

		smp_mb();



	return !contended;

}



static inline void arch_spin_unlock(arch_spinlock_t *lock)

{

	smp_mb();

	WRITE_ONCE(lock->tickets.owner, lock->tickets.owner + 1);

}



static inline int arch_spin_value_unlocked(arch_spinlock_t lock)

{

	return lock.tickets.owner == lock.tickets.next;

}



static inline int arch_spin_is_locked(arch_spinlock_t *lock)

{

	return !arch_spin_value_unlocked(READ_ONCE(*lock));

}



static inline int arch_spin_is_contended(arch_spinlock_t *lock)

{

	struct __raw_tickets tickets = READ_ONCE(lock->tickets);



	return (tickets.next - tickets.owner) > 1;

}

#define arch_spin_is_contended	arch_spin_is_contended



#include <asm/qrwlock.h>



#endif /* __ASM_CSKY_SPINLOCK_H */

arch/csky/include/asm/spinlock_types.h

deleted100644 → 0
+0 −27
Original line number Diff line number Diff line 
/* SPDX-License-Identifier: GPL-2.0 */



#ifndef __ASM_CSKY_SPINLOCK_TYPES_H

#define __ASM_CSKY_SPINLOCK_TYPES_H



#ifndef __LINUX_SPINLOCK_TYPES_RAW_H

# error "please don't include this file directly"

#endif



#define TICKET_NEXT	16



typedef struct {

	union {

		u32 lock;

		struct __raw_tickets {

			/* little endian */

			u16 owner;

			u16 next;

		} tickets;

	};

} arch_spinlock_t;



#define __ARCH_SPIN_LOCK_UNLOCKED	{ { 0 } }



#include <asm-generic/qrwlock_types.h>



#endif /* __ASM_CSKY_SPINLOCK_TYPES_H */

arch/openrisc/Kconfig

+0 −1
Original line number Diff line number Diff line
@@ -30,7 +30,6 @@ config OPENRISC 
	select HAVE_DEBUG_STACKOVERFLOW

	select OR1K_PIC

	select CPU_NO_EFFICIENT_FFS if !OPENRISC_HAVE_INST_FF1

	select ARCH_USE_QUEUED_SPINLOCKS

	select ARCH_USE_QUEUED_RWLOCKS

	select OMPIC if SMP

	select ARCH_WANT_FRAME_POINTERS

arch/openrisc/include/asm/Kbuild

+2 −3
Original line number Diff line number Diff line 
# SPDX-License-Identifier: GPL-2.0

generic-y += extable.h

generic-y += kvm_para.h

generic-y += mcs_spinlock.h

generic-y += qspinlock_types.h

generic-y += qspinlock.h

generic-y += spinlock_types.h

generic-y += spinlock.h

generic-y += qrwlock_types.h

generic-y += qrwlock.h

generic-y += user.h