Re: perf record doesn't work on rtd129x SoC

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On 2019-12-04 11:20, Robin Murphy wrote:
On 2019-12-04 7:28 am, Andreas Färber wrote:
Hi YanQing,
+ LAKML + Mark + Will
Am 04.12.19 um 05:55 schrieb Wang YanQing:
I use "perf record" to debug performance issue on RTD1296 SOC, it does't work, but
the "perf stat" is ok!
Thanks for the report - which board, branch and (base) tag are you
testing against? And are you building perf yourself from kernel sources,
or are you using some distro package?
I only have Busybox in my initrd on DS418; I have not tested perf.

After some dig in the kernel, I find the reason is no pmu overflow interrupt, I think
below pmu configuration isn't right for RTD1296:
         arm_pmu: arm-pmu {
                 compatible = "arm,cortex-a53-pmu";
                 interrupts = <GIC_SPI 48 IRQ_TYPE_LEVEL_HIGH>;

We need 4 PMU SPI for RTD1296 (4 cores), and I guess the 48 isn't right too.
Note that above rtd129x.dtsi snippet is not complete. See rtd1296.dtsi:
&arm_pmu {
	interrupt-affinity = <&cpu0>, <&cpu1>, <&cpu2>, <&cpu3>;

That doesn't help much, since 4 affinities for one SPI is rather nonsensical.

48 and high/4 match what I see in the latest BSP:

Any suggestion is welcome.

The only difference I see is "arm,cortex-a53-pmu" vs. "arm,armv8-pmuv3".
By my reading of arch/arm64/kernel/perf_event.c the only difference
between the two should be the name and an extra cache_map. You could try
the other compatible string in your .dts, but I doubt it'll help.
Hopefully the Realtek or Arm guys can shed some light.

If the SoC really has all 4 overflow interrupts combined into a
single SPI line, then sampling just isn't going to be supported - it's unreasonably difficult to handle overflow when the IRQ may be taken on
the wrong CPU.

Indeed. And I've recently found this exact design blunder on a brand new
Amlogic SoC, where the per-core interrupts have been OR'd together.
And not just for the PMU! It is the same situation for the GIC, CTI,
and a couple of other things. The only sane interrupts are the timers.

(sound of a PCB hitting the bin...)

Jazz is not dead. It just smells funny...

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