RE: [PATCH RFC v3 00/12] perf pmu-events: Support event aliasing for system PMUs

[Joakim Zhang]

> -----Original Message-----
> From: John Garry <john.garry@xxxxxxxxxx>
> Sent: 2020年5月12日 18:13
> To: Joakim Zhang <qiangqing.zhang@xxxxxxx>; peterz@xxxxxxxxxxxxx;
> mingo@xxxxxxxxxx; acme@xxxxxxxxxx; mark.rutland@xxxxxxx;
> alexander.shishkin@xxxxxxxxxxxxxxx; jolsa@xxxxxxxxxx;
> namhyung@xxxxxxxxxx
> Cc: irogers@xxxxxxxxxx; ak@xxxxxxxxxxxxxxx; robin.murphy@xxxxxxx;
> Linuxarm <linuxarm@xxxxxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx;
> Zhangshaokun <zhangshaokun@xxxxxxxxxxxxx>; will@xxxxxxxxxx;
> linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [PATCH RFC v3 00/12] perf pmu-events: Support event aliasing for
> system PMUs
> 
> 
> > I have an aside question, do you have any idea? Thanks a lot!
> >
> > For DDR PMU, I want to add bandwidth usage metric, but it depends on DDR
> controller clock frequency.
> > For example, we have i.MX8MM LPDDR4 board which DDR controller clock is
> 800MHZ, and i.MX8MM DDR4 board which DDR controller is 600MHZ, but the
> SoC is the same.
> >
> > So they can share all JSON metrics with identifier "i.mx8mm", except
> bandwidth metric.
>
> what is the bandwidth metric? how is it supposed to be calculated?

Something like below to calculate bandwidth usage:

i.MX8MM LPDDR4 board:  ((read-cycles + write-cycles) * 4 * 4 / duration_time) / (800 * 1000000 * 4 * 4)
i.MX8MM DDR4 board:  ((read-cycles + write-cycles) * 4 * 4 / duration_time) / (600 * 1000000 * 4 * 4)

So this should not be Soc specific, it is board specific, I don't know how to implement it from metric.

> If I add separate JOSN metrics files for identifier "i.mx8mm-lpddr4" and
> identifier "i.mx8mm-ddr4", then it's going to be very redundant, since most
> metrics are same just the identifier is different.
> >
> > Do you know how perf tool handle such case?
> 
> jirka is supporting user-defined metric here:
> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.ker
> nel.org%2Flkml%2F20200511205307.3107775-1-jolsa%40kernel.org%2F&amp;
> data=02%7C01%7Cqiangqing.zhang%40nxp.com%7Cbbd26d737cf44896ed360
> 8d7f65d33ad%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C637248
> 752464922384&amp;sdata=wGqQ4%2B6rejJYrDj0SzeGJn09r660QIzOvRy0DCw
> EGVQ%3D&amp;reserved=0
> 
> So maybe you can use that somehow with separate scripts.

Thanks for your hint, I will research it to see if it is possible.

Best Regards,
Joakim Zhang
> Thanks,
> John