Question: SMMUv3 PMU event aliasing

[Robin Murphy]

On 2021-11-08 12:41, John Garry wrote:
> On 08/11/2021 12:19, Leo Yan wrote:
>> Hi John,
>>
>> [ + mailing list ]
> 
> Hi Leo,
> 
>>
>> I'd like to confirm the latest upstream status for SMMUv3 PMU event
>> aliasing.
>>
>> I see the patch set v6 of "perf pmu-events: Support event aliasing for
>> system PMUs" [1] has been landed on the mainline kernel, and as an
>> example, imx8mm DDR PMU has been supported as system PMU [2].
>>
>> On the other hand, I can see patch set 5 contains the SMMUv3 PMU event
>> aliasing with patch "perf vendor events arm64: Add Architected events
>> smmuv3-pmcg.json" [3], but this patch was left out in patch set 6 and
>> it's never landed on the mainline kernel.
>>
>> Could you share current status (or plan) for upstreaming SMMUv3 PMU
>> event alias?  Or if there have any block issue to prevent merging the
>> changes in the mainline kernel?
> 
> This feature should be supported in the SMMUv3 PMU kernel driver and 
> perf tool.
> 
> However it relies on the SMMU PMU identifier sysfs file to work. This 
> relies on SMMU_PMCG_IIDR being set, which is introduced latest spec, 
> which not much HW will support yet - see commit 2c255223362e. In theory 
> we don't need that for the fixed, non-IMPDEF events, but I did not 
> complicate perf tool with that mixed support.
> 
> That's the reason for which I paused smmuv3-pmcg.json upstream in [3]. I 
> will revive that for new gen HW when concrete IMPDEF events known and 
> shared.

FWIW, imp-def-events are readily available for the existing Arm 
implementations[1][2], and annoyingly we could trivially synthesise an 
IIDR value from their imp-def PIDR registers if only we knew that that 
was valid to do in the first place. I feel tempted now to resurrect 
Jean-Philippe's DT binding and have a quick hack at that, then maybe a 
much longer think about how to attempt it for IORT...

Cheers,
Robin.

[1] 
https://developer.arm.com/documentation/100310/0202/Functional-description/Operation/Performance-Monitoring-Unit
[2] 
https://developer.arm.com/documentation/101542/0001/Functional-description/Operation/Performance-Monitoring-Unit

> 
> Thanks,
> John
> 
>>
>> Thanks for your help!
>>
>> Leo
>>
>> [1] 
>> https://lore.kernel.org/lkml/1607080216-36968-1-git-send-email-john.garry@huawei.com/ 
>>
>> [2] pmu-events/arch/arm64/freescale/imx8mm/sys/ddrc.json
>> [3] 
>> https://lore.kernel.org/lkml/1604666153-4187-6-git-send-email-john.garry@huawei.com/ 
>>
>> .
>>
> 
> 
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