Re: [PATCH RFC 0/7] perf pmu-events: Support event aliasing for system PMUs

[John Garry]

> > > i.MX8MM and i.MX8MN, they use the same driver(DDRC_ID) and cortex-a53
> > integrated.
> > > If we want to monitor VPU, their *master id* is different from SoCs.
> > > On i.MX8MM, event is imx8_ddr0/axid-read,axi_id=0x08/ On i.MX8MN,
> > > event is imx8_ddr0/axid-read,axi_id=0x12/

So it seems that this master id and the axi_id are the same, which is 
some filtering key. Indeed, the actual event number is the same between 
SoC implementations.

And metric groups do support filtering, AFAIU.

> > > I try to write a JSON file to use these events, for now, I only can
> > > locate the file at the directory:
> > > tools/perf/pmu-events/arch/arm64/arm/cortex-a53/
> > >
> > > Perf tool loads all events when CPUID matched, which is now unreasonable,
> > we want related events are loaded for specific SoC.
> >
> > so we could have a folder like .../arch/arm64/nxp/system for these JSONs. The
> > perf tool can be updated to handle CPU and system events in separate folders.
> >
> > > All events will also be loaded if we use DDRC_ID to match in the future, this
> > seems to not be a good ideal.
> >
> > The important part is knowing which events are supported per implementation.
> > Is there any method in the driver of knowing the specific implementation, like
> > any DT compat string? Least preferred option would be DT machine ID.
>
> I think, NO, master id could be different even they use the same DT compatible string.

Are you sure? Checking the dts files for your SoCs, I see this:

~/kernel-dev6/arch/arm64$ git grep  "fsl,imx8m-ddr-pmu"
boot/dts/freescale/imx8mm.dtsi:                 compatible = 
"fsl,imx8mm-ddr-pmu", "fsl,imx8m-ddr-pmu";
boot/dts/freescale/imx8mn.dtsi:                 compatible = 
"fsl,imx8mn-ddr-pmu", "fsl,imx8m-ddr-pmu";
boot/dts/freescale/imx8mq.dtsi:                 compatible = 
"fsl,imx8mq-ddr-pmu", "fsl,imx8m-ddr-pmu";

So it seems that you could use "fsl,imx8mm-ddr-pmu" vs 
"fsl,imx8mn-ddr-pmu" to differentiate, right?

John