Commit 20c0e826 authored by Nicholas Piggin's avatar Nicholas Piggin Committed by Michael Ellerman
Browse files

powerpc/pseries: Implement paravirt qspinlocks for SPLPAR 



This implements the generic paravirt qspinlocks using H_PROD and
H_CONFER to kick and wait.

This uses an un-directed yield to any CPU rather than the directed
yield to a pre-empted lock holder that paravirtualised simple
spinlocks use, that requires no kick hcall. This is something that
could be investigated and improved in future.

Performance results can be found in the commit which added queued
spinlocks.

Signed-off-by: default avatarNicholas Piggin <npiggin@gmail.com>
Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: default avatarWaiman Long <longman@redhat.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200724131423.1362108-5-npiggin@gmail.com
parent aa65ff6b

arch/powerpc/include/asm/paravirt.h

+28 −0
Original line number Diff line number Diff line
@@ -28,6 +28,16 @@ static inline void yield_to_preempted(int cpu, u32 yield_count) 
{

	plpar_hcall_norets(H_CONFER, get_hard_smp_processor_id(cpu), yield_count);

}



static inline void prod_cpu(int cpu)

{

	plpar_hcall_norets(H_PROD, get_hard_smp_processor_id(cpu));

}



static inline void yield_to_any(void)

{

	plpar_hcall_norets(H_CONFER, -1, 0);

}

#else

static inline bool is_shared_processor(void)

{
@@ -44,6 +54,19 @@ static inline void yield_to_preempted(int cpu, u32 yield_count) 
{

	___bad_yield_to_preempted(); /* This would be a bug */

}



extern void ___bad_yield_to_any(void);

static inline void yield_to_any(void)

{

	___bad_yield_to_any(); /* This would be a bug */

}



extern void ___bad_prod_cpu(void);

static inline void prod_cpu(int cpu)

{

	___bad_prod_cpu(); /* This would be a bug */

}



#endif



#define vcpu_is_preempted vcpu_is_preempted
@@ -56,4 +79,9 @@ static inline bool vcpu_is_preempted(int cpu) 
	return false;

}



static inline bool pv_is_native_spin_unlock(void)

{

	return !is_shared_processor();

}



#endif /* _ASM_POWERPC_PARAVIRT_H */

arch/powerpc/include/asm/qspinlock.h

+66 −0
Original line number Diff line number Diff line
@@ -3,9 +3,47 @@ 
#define _ASM_POWERPC_QSPINLOCK_H



#include <asm-generic/qspinlock_types.h>

#include <asm/paravirt.h>



#define _Q_PENDING_LOOPS	(1 << 9) /* not tuned */



#ifdef CONFIG_PARAVIRT_SPINLOCKS

extern void native_queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);

extern void __pv_queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);

extern void __pv_queued_spin_unlock(struct qspinlock *lock);



static __always_inline void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)

{

	if (!is_shared_processor())

		native_queued_spin_lock_slowpath(lock, val);

	else

		__pv_queued_spin_lock_slowpath(lock, val);

}



#define queued_spin_unlock queued_spin_unlock

static inline void queued_spin_unlock(struct qspinlock *lock)

{

	if (!is_shared_processor())

		smp_store_release(&lock->locked, 0);

	else

		__pv_queued_spin_unlock(lock);

}



#else

extern void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);

#endif



static __always_inline void queued_spin_lock(struct qspinlock *lock)

{

	u32 val = 0;



	if (likely(atomic_try_cmpxchg_acquire(&lock->val, &val, _Q_LOCKED_VAL)))

		return;



	queued_spin_lock_slowpath(lock, val);

}

#define queued_spin_lock queued_spin_lock



#define smp_mb__after_spinlock()   smp_mb()



static __always_inline int queued_spin_is_locked(struct qspinlock *lock)
@@ -20,6 +58,34 @@ static __always_inline int queued_spin_is_locked(struct qspinlock *lock) 
}

#define queued_spin_is_locked queued_spin_is_locked



#ifdef CONFIG_PARAVIRT_SPINLOCKS

#define SPIN_THRESHOLD (1<<15) /* not tuned */



static __always_inline void pv_wait(u8 *ptr, u8 val)

{

	if (*ptr != val)

		return;

	yield_to_any();

	/*

	 * We could pass in a CPU here if waiting in the queue and yield to

	 * the previous CPU in the queue.

	 */

}



static __always_inline void pv_kick(int cpu)

{

	prod_cpu(cpu);

}



extern void __pv_init_lock_hash(void);



static inline void pv_spinlocks_init(void)

{

	__pv_init_lock_hash();

}



#endif



#include <asm-generic/qspinlock.h>



#endif /* _ASM_POWERPC_QSPINLOCK_H */

arch/powerpc/include/asm/qspinlock_paravirt.h

0 → 100644
+7 −0
Original line number Diff line number Diff line 
/* SPDX-License-Identifier: GPL-2.0-or-later */

#ifndef _ASM_POWERPC_QSPINLOCK_PARAVIRT_H

#define _ASM_POWERPC_QSPINLOCK_PARAVIRT_H



EXPORT_SYMBOL(__pv_queued_spin_unlock);



#endif /* _ASM_POWERPC_QSPINLOCK_PARAVIRT_H */

arch/powerpc/include/asm/spinlock.h

+4 −0
Original line number Diff line number Diff line
@@ -10,5 +10,9 @@ 
#include <asm/simple_spinlock.h>

#endif



#ifndef CONFIG_PARAVIRT_SPINLOCKS

static inline void pv_spinlocks_init(void) { }

#endif



#endif /* __KERNEL__ */

#endif /* __ASM_SPINLOCK_H */

arch/powerpc/platforms/pseries/Kconfig

+8 −1
Original line number Diff line number Diff line
@@ -25,15 +25,22 @@ config PPC_PSERIES 
	select SWIOTLB

	default y



config PARAVIRT_SPINLOCKS

	bool



config PPC_SPLPAR

	depends on PPC_PSERIES

	bool "Support for shared-processor logical partitions"

	depends on PPC_PSERIES

	select PARAVIRT_SPINLOCKS if PPC_QUEUED_SPINLOCKS

	default y

	help

	  Enabling this option will make the kernel run more efficiently

	  on logically-partitioned pSeries systems which use shared

	  processors, that is, which share physical processors between

	  two or more partitions.



	  Say Y if you are unsure.



config DTL

	bool "Dispatch Trace Log"

	depends on PPC_SPLPAR && DEBUG_FS

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