Commit 5a7745b9 authored by Nicholas Piggin's avatar Nicholas Piggin Committed by Michael Ellerman
Browse files

powerpc/64s/perf: add power_pmu_wants_prompt_pmi to say whether perf wants PMIs to be soft-NMI 



Interrupt code enables MSR[EE] in some irq handlers while keeping local
irqs disabled via soft-mask, allowing PMI interrupts to be taken as
soft-NMI to improve profiling of irq handlers.

When perf is not enabled, there is no point to doing this, it's
additional overhead. So provide a function that can say if PMIs should
be taken promptly if possible.

Signed-off-by: default avatarNicholas Piggin <npiggin@gmail.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210922145452.352571-4-npiggin@gmail.com
parent ff0b0d6e

arch/powerpc/include/asm/hw_irq.h

+2 −0
Original line number Diff line number Diff line
@@ -342,6 +342,8 @@ static inline bool lazy_irq_pending_nocheck(void) 
	return __lazy_irq_pending(local_paca->irq_happened);

}



bool power_pmu_wants_prompt_pmi(void);



/*

 * This is called by asynchronous interrupts to conditionally

 * re-enable hard interrupts after having cleared the source

arch/powerpc/perf/core-book3s.c

+31 −0
Original line number Diff line number Diff line
@@ -17,6 +17,7 @@ 
#include <asm/firmware.h>

#include <asm/ptrace.h>

#include <asm/code-patching.h>

#include <asm/hw_irq.h>

#include <asm/interrupt.h>



#ifdef CONFIG_PPC64
@@ -2437,6 +2438,36 @@ static void perf_event_interrupt(struct pt_regs *regs) 
	perf_sample_event_took(sched_clock() - start_clock);

}



/*

 * If the perf subsystem wants performance monitor interrupts as soon as

 * possible (e.g., to sample the instruction address and stack chain),

 * this should return true. The IRQ masking code can then enable MSR[EE]

 * in some places (e.g., interrupt handlers) that allows PMI interrupts

 * though to improve accuracy of profiles, at the cost of some performance.

 *

 * The PMU counters can be enabled by other means (e.g., sysfs raw SPR

 * access), but in that case there is no need for prompt PMI handling.

 *

 * This currently returns true if any perf counter is being used. It

 * could possibly return false if only events are being counted rather than

 * samples being taken, but for now this is good enough.

 */

bool power_pmu_wants_prompt_pmi(void)

{

	struct cpu_hw_events *cpuhw;



	/*

	 * This could simply test local_paca->pmcregs_in_use if that were not

	 * under ifdef KVM.

	 */



	if (!ppmu)

		return false;



	cpuhw = this_cpu_ptr(&cpu_hw_events);

	return cpuhw->n_events;

}



static int power_pmu_prepare_cpu(unsigned int cpu)

{

	struct cpu_hw_events *cpuhw = &per_cpu(cpu_hw_events, cpu);