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From: Michael Ellerman <mpe@ellerman.id.au>
To: Nicholas Piggin <npiggin@gmail.com>, linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH v1 2/4] powerpc/64s/perf: add power_pmu_running to query
 whether perf is being used
In-Reply-To: <20210816072953.1165964-3-npiggin@gmail.com>
References: <20210816072953.1165964-1-npiggin@gmail.com>
 <20210816072953.1165964-3-npiggin@gmail.com>
Date: Tue, 17 Aug 2021 23:42:05 +1000
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Cc: Athira Rajeev <atrajeev@linux.vnet.ibm.com>,
 Madhavan Srinivasan <maddy@linux.ibm.com>, Nicholas Piggin <npiggin@gmail.com>
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 <linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org>

Nicholas Piggin <npiggin@gmail.com> writes:

> Interrupt handling code would like to know whether perf is enabled, to
> know whether it should enable MSR[EE] to improve PMI coverage.
>
> Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
> Cc: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> ---
>  arch/powerpc/include/asm/hw_irq.h |  2 ++
>  arch/powerpc/perf/core-book3s.c   | 13 +++++++++++++
>  2 files changed, 15 insertions(+)
>
> diff --git a/arch/powerpc/include/asm/hw_irq.h b/arch/powerpc/include/asm/hw_irq.h
> index 21cc571ea9c2..2d5c0d3ccbb6 100644
> --- a/arch/powerpc/include/asm/hw_irq.h
> +++ b/arch/powerpc/include/asm/hw_irq.h
> @@ -306,6 +306,8 @@ static inline bool lazy_irq_pending_nocheck(void)
>  	return __lazy_irq_pending(local_paca->irq_happened);
>  }
>  
> +bool power_pmu_running(void);
> +
>  /*
>   * This is called by asynchronous interrupts to conditionally
>   * re-enable hard interrupts after having cleared the source
> diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
> index bb0ee716de91..76114a9afb2b 100644
> --- a/arch/powerpc/perf/core-book3s.c
> +++ b/arch/powerpc/perf/core-book3s.c
> @@ -2380,6 +2380,19 @@ static void perf_event_interrupt(struct pt_regs *regs)
>  	perf_sample_event_took(sched_clock() - start_clock);
>  }
>  
> +bool power_pmu_running(void)
> +{
> +	struct cpu_hw_events *cpuhw;
> +
> +	/* Could this simply test local_paca->pmcregs_in_use? */

I think it could, except that it's under an ifdef:

#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
	u8 pmcregs_in_use;		/* pseries puts this in lppaca */
#endif

cheers