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Commit 93a6d3ce authored by Paul Mackerras's avatar Paul Mackerras
Browse files

powerpc: Provide a way to defer perf counter work until interrupts are enabled 



Because 64-bit powerpc uses lazy (soft) interrupt disabling, it is
possible for a performance monitor exception to come in when the
kernel thinks interrupts are disabled (i.e. when they are
soft-disabled but hard-enabled).  In such a situation the performance
monitor exception handler might have some processing to do (such as
process wakeups) which can't be done in what is effectively an NMI
handler.

This provides a way to defer that work until interrupts get enabled,
either in raw_local_irq_restore() or by returning from an interrupt
handler to code that had interrupts enabled.  We have a per-processor
flag that indicates that there is work pending to do when interrupts
subsequently get re-enabled.  This flag is checked in the interrupt
return path and in raw_local_irq_restore(), and if it is set,
perf_counter_do_pending() is called to do the pending work.

Signed-off-by: default avatarPaul Mackerras <paulus@samba.org>
parent d662ed26

arch/powerpc/include/asm/hw_irq.h

+31 −0
Original line number Diff line number Diff line
@@ -131,5 +131,36 @@ static inline int irqs_disabled_flags(unsigned long flags) 
 */

struct hw_interrupt_type;



#ifdef CONFIG_PERF_COUNTERS

static inline unsigned long get_perf_counter_pending(void)

{

	unsigned long x;



	asm volatile("lbz %0,%1(13)"

		: "=r" (x)

		: "i" (offsetof(struct paca_struct, perf_counter_pending)));

	return x;

}



static inline void set_perf_counter_pending(int x)

{

	asm volatile("stb %0,%1(13)" : :

		"r" (x),

		"i" (offsetof(struct paca_struct, perf_counter_pending)));

}



extern void perf_counter_do_pending(void);



#else



static inline unsigned long get_perf_counter_pending(void)

{

	return 0;

}



static inline void set_perf_counter_pending(int x) {}

static inline void perf_counter_do_pending(void) {}

#endif /* CONFIG_PERF_COUNTERS */



#endif	/* __KERNEL__ */

#endif	/* _ASM_POWERPC_HW_IRQ_H */

arch/powerpc/include/asm/paca.h

+1 −0
Original line number Diff line number Diff line
@@ -99,6 +99,7 @@ struct paca_struct { 
	u8 soft_enabled;		/* irq soft-enable flag */

	u8 hard_enabled;		/* set if irqs are enabled in MSR */

	u8 io_sync;			/* writel() needs spin_unlock sync */

	u8 perf_counter_pending;	/* PM interrupt while soft-disabled */



	/* Stuff for accurate time accounting */

	u64 user_time;			/* accumulated usermode TB ticks */

arch/powerpc/kernel/asm-offsets.c

+1 −0
Original line number Diff line number Diff line
@@ -127,6 +127,7 @@ int main(void) 
	DEFINE(PACAKMSR, offsetof(struct paca_struct, kernel_msr));

	DEFINE(PACASOFTIRQEN, offsetof(struct paca_struct, soft_enabled));

	DEFINE(PACAHARDIRQEN, offsetof(struct paca_struct, hard_enabled));

	DEFINE(PACAPERFPEND, offsetof(struct paca_struct, perf_counter_pending));

	DEFINE(PACASLBCACHE, offsetof(struct paca_struct, slb_cache));

	DEFINE(PACASLBCACHEPTR, offsetof(struct paca_struct, slb_cache_ptr));

	DEFINE(PACACONTEXTID, offsetof(struct paca_struct, context.id));

arch/powerpc/kernel/entry_64.S

+9 −0
Original line number Diff line number Diff line
@@ -526,6 +526,15 @@ ALT_FW_FTR_SECTION_END_IFCLR(FW_FEATURE_ISERIES) 
2:

	TRACE_AND_RESTORE_IRQ(r5);



#ifdef CONFIG_PERF_COUNTERS

	/* check paca->perf_counter_pending if we're enabling ints */

	lbz	r3,PACAPERFPEND(r13)

	and.	r3,r3,r5

	beq	27f

	bl	.perf_counter_do_pending

27:

#endif /* CONFIG_PERF_COUNTERS */



	/* extract EE bit and use it to restore paca->hard_enabled */

	ld	r3,_MSR(r1)

	rldicl	r4,r3,49,63		/* r0 = (r3 >> 15) & 1 */

arch/powerpc/kernel/irq.c

+10 −0
Original line number Diff line number Diff line
@@ -104,6 +104,13 @@ static inline notrace void set_soft_enabled(unsigned long enable) 
	: : "r" (enable), "i" (offsetof(struct paca_struct, soft_enabled)));

}



#ifdef CONFIG_PERF_COUNTERS

notrace void __weak perf_counter_do_pending(void)

{

	set_perf_counter_pending(0);

}

#endif



notrace void raw_local_irq_restore(unsigned long en)

{

	/*
@@ -135,6 +142,9 @@ notrace void raw_local_irq_restore(unsigned long en) 
			iseries_handle_interrupts();

	}



	if (get_perf_counter_pending())

		perf_counter_do_pending();



	/*

	 * if (get_paca()->hard_enabled) return;

	 * But again we need to take care that gcc gets hard_enabled directly