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From: Robin Murphy <robin.murphy@arm.com>
To: Ilkka Koskinen <ilkka@os.amperecomputing.com>
Cc: Jonathan Corbet <corbet@lwn.net>, Will Deacon <will@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Besar Wicaksono <bwicaksono@nvidia.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v2 2/5] perf: arm_cspmu: Support shared interrupts
Date: Fri, 2 Jun 2023 12:25:53 +0100	[thread overview]
Message-ID: <4bc59e32-a3cc-4e8c-0264-e509aadeb534@arm.com> (raw)
In-Reply-To: <77b19b2d-a84e-eb13-db38-78cb34a444a8@os.amperecomputing.com>

On 2023-06-02 08:04, Ilkka Koskinen wrote:
> 
> Hi Robin,
> 
> On Thu, 1 Jun 2023, Robin Murphy wrote:
>> 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.
> 
> I see, I wasn't aware of such an assumption. Sounds like there isn't 
> necessarily an easy and clean solution for the shared interrupt case. I 
> drop the patch and get back on the issue if we come up with something 
> reasonable later.

What comes to mind is factoring out the explicit interrupt-sharing 
machinery that we wrote to solve this problem in arm_dmc620_pmu, or 
possibly trying to do something with IRQ affinity notifiers (however, I 
recall looking into that a while ago and it didn't seem like they 
actually interact with CPU hotplug in the way we'd want).

Thanks,
Robin.

WARNING: multiple messages have this Message-ID (diff)
From: Robin Murphy <robin.murphy@arm.com>
To: Ilkka Koskinen <ilkka@os.amperecomputing.com>
Cc: Jonathan Corbet <corbet@lwn.net>, Will Deacon <will@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Besar Wicaksono <bwicaksono@nvidia.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v2 2/5] perf: arm_cspmu: Support shared interrupts
Date: Fri, 2 Jun 2023 12:25:53 +0100	[thread overview]
Message-ID: <4bc59e32-a3cc-4e8c-0264-e509aadeb534@arm.com> (raw)
In-Reply-To: <77b19b2d-a84e-eb13-db38-78cb34a444a8@os.amperecomputing.com>

On 2023-06-02 08:04, Ilkka Koskinen wrote:
> 
> Hi Robin,
> 
> On Thu, 1 Jun 2023, Robin Murphy wrote:
>> 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.
> 
> I see, I wasn't aware of such an assumption. Sounds like there isn't 
> necessarily an easy and clean solution for the shared interrupt case. I 
> drop the patch and get back on the issue if we come up with something 
> reasonable later.

What comes to mind is factoring out the explicit interrupt-sharing 
machinery that we wrote to solve this problem in arm_dmc620_pmu, or 
possibly trying to do something with IRQ affinity notifiers (however, I 
recall looking into that a while ago and it didn't seem like they 
actually interact with CPU hotplug in the way we'd want).

Thanks,
Robin.

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  reply	other threads:[~2023-06-02 11:26 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-06-01  3:01 [PATCH v2 0/5] perf: ampere: Add support for Ampere SoC PMUs Ilkka Koskinen
2023-06-01  3:01 ` Ilkka Koskinen
2023-06-01  3:01 ` [PATCH v2 1/5] perf: arm_cspmu: Support 32-bit accesses to 64-bit registers Ilkka Koskinen
2023-06-01  3:01   ` Ilkka Koskinen
2023-06-01 14:49   ` Robin Murphy
2023-06-01 14:49     ` Robin Murphy
2023-06-02  6:47     ` Ilkka Koskinen
2023-06-02  6:47       ` Ilkka Koskinen
2023-06-01  3:01 ` [PATCH v2 2/5] perf: arm_cspmu: Support shared interrupts Ilkka Koskinen
2023-06-01  3:01   ` Ilkka Koskinen
2023-06-01 14:54   ` Robin Murphy
2023-06-01 14:54     ` Robin Murphy
2023-06-02  7:04     ` Ilkka Koskinen
2023-06-02  7:04       ` Ilkka Koskinen
2023-06-02 11:25       ` Robin Murphy [this message]
2023-06-02 11:25         ` Robin Murphy
2023-06-01  3:01 ` [PATCH v2 3/5] perf: arm_cspmu: Support implementation specific filters Ilkka Koskinen
2023-06-01  3:01   ` Ilkka Koskinen
2023-06-01  3:01 ` [PATCH v2 4/5] perf: arm_cspmu: Support implementation specific event validation Ilkka Koskinen
2023-06-01  3:01   ` Ilkka Koskinen
2023-06-01 15:09   ` Robin Murphy
2023-06-01 15:09     ` Robin Murphy
2023-06-02  7:09     ` Ilkka Koskinen
2023-06-02  7:09       ` Ilkka Koskinen
2023-06-01  3:01 ` [PATCH v2 5/5] perf: arm_cspmu: ampere_cspmu: Add support for Ampere SoC PMU Ilkka Koskinen
2023-06-01  3:01   ` Ilkka Koskinen
2023-06-01 15:23   ` Robin Murphy
2023-06-01 15:23     ` Robin Murphy
2023-06-02  7:13     ` Ilkka Koskinen
2023-06-02  7:13       ` Ilkka Koskinen
2023-06-02 11:51       ` Robin Murphy
2023-06-02 11:51         ` Robin Murphy
2023-06-03  1:16   ` kernel test robot
2023-06-03  1:16     ` kernel test robot

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