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Subject: Re: [RFC PATCH] perf/smmuv3: Fix shared interrupt handling
To:     Robin Murphy <robin.murphy@arm.com>,
        "will@kernel.org" <will@kernel.org>,
        "mark.rutland@arm.com" <mark.rutland@arm.com>
CC:     "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        Shameerali Kolothum Thodi 
        <shameerali.kolothum.thodi@huawei.com>,
        "harb@amperecomputing.com" <harb@amperecomputing.com>,
        "tuanphan@os.amperecomputing.com" <tuanphan@os.amperecomputing.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
References: <d73dd8c3579fbf713d6215317404549aede8ad2d.1586363449.git.robin.murphy@arm.com>
From:   John Garry <john.garry@huawei.com>
Message-ID: <34dd7c2e-b6db-684f-f0a2-73f2e6951308@huawei.com>
Date:   Thu, 9 Apr 2020 08:02:20 +0100
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On 08/04/2020 17:49, Robin Murphy wrote:
> IRQF_SHARED is dangerous, since it allows other agents to retarget the
> IRQ's affinity without migrating PMU contexts to match, breaking the way
> in which perf manages mutual exclusion for accessing events. Although
> this means it's not realistically possible to support PMU IRQs being
> shared with other drivers, we *can* handle sharing between multiple PMU
> instances with some explicit affinity bookkeeping and manual interrupt
> multiplexing.

Hi Robin,

Out of curiosity, do we even need to support shared interrupts for any 
implementations today?

D06 board:

john@ubuntu:~$ more /proc/interrupts | grep smmuv3-pmu

  989:  0  0  0  0  ITS-pMSI 133120 Edge  smmuv3-pmu
  990:  0  0  0  0  ITS-pMSI 135168 Edge  smmuv3-pmu
  991:  0  0  0  0  ITS-pMSI 137216 Edge  smmuv3-pmu
  992:  0  0  0  0  ITS-pMSI 139264 Edge  smmuv3-pmu
  993:  0  0  0  0  ITS-pMSI 141312 Edge  smmuv3-pmu
  994:  0  0  0  0  ITS-pMSI 143360 Edge  smmuv3-pmu
  995:  0  0  0  0  ITS-pMSI 145408 Edge  smmuv3-pmu
  996:  0  0  0  0  ITS-pMSI 147456 Edge  smmuv3-pmu

Thanks,
John