linux-kernel - Re: [PATCH v2 2/5] perf: arm_cspmu: Support shared interrupts

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Message-ID: <e2f2c524-c7c5-7a55-aee5-699b069a445a@arm.com>
Date:   Thu, 1 Jun 2023 15:54:03 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Ilkka Koskinen <ilkka@...amperecomputing.com>,
        Jonathan Corbet <corbet@....net>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Besar Wicaksono <bwicaksono@...dia.com>,
        Suzuki K Poulose <suzuki.poulose@....com>
Cc:     linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 2/5] perf: arm_cspmu: Support shared interrupts

On 2023-06-01 04:01, Ilkka Koskinen wrote:
> Some of the PMUs may share the interrupt. Support them by
> setting IRQF_SHARED

This has the usual problem of allowing any PMU instance to move the IRQ 
affinity to a different CPU without also migrating all the other PMU 
contexts, and thus breaking perf core's assumptions of mutual exclusion.

Thanks,
Robin.

> Signed-off-by: Ilkka Koskinen <ilkka@...amperecomputing.com>
> ---
>   drivers/perf/arm_cspmu/arm_cspmu.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/perf/arm_cspmu/arm_cspmu.c b/drivers/perf/arm_cspmu/arm_cspmu.c
> index 88547a2b73e6..cc5204d1b5fb 100644
> --- a/drivers/perf/arm_cspmu/arm_cspmu.c
> +++ b/drivers/perf/arm_cspmu/arm_cspmu.c
> @@ -1067,8 +1067,8 @@ static int arm_cspmu_request_irq(struct arm_cspmu *cspmu)
>   		return irq;
>   
>   	ret = devm_request_irq(dev, irq, arm_cspmu_handle_irq,
> -			       IRQF_NOBALANCING | IRQF_NO_THREAD, dev_name(dev),
> -			       cspmu);
> +			       IRQF_NOBALANCING | IRQF_NO_THREAD | IRQF_SHARED,
> +			       dev_name(dev), cspmu);
>   	if (ret) {
>   		dev_err(dev, "Could not request IRQ %d\n", irq);
>   		return ret;