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

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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: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210922145452.352571-4-npiggin@gmail.com
This commit is contained in:
Nicholas Piggin 2021-09-23 00:54:49 +10:00 committed by Michael Ellerman
parent ff0b0d6e1a
commit 5a7745b96f
2 changed files with 33 additions and 0 deletions
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2
arch/powerpc/include/asm/hw_irq.h
View File

@ -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

31
arch/powerpc/perf/core-book3s.c
View File

@ -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);