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SubjectRe: perf record doesn't work on rtd129x SoC
On Wed, Dec 04, 2019 at 02:51:24PM +0000, Robin Murphy wrote:
> On 04/12/2019 11:20 am, 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:
> >>
> >> https://github.com/BPI-SINOVOIP/BPI-M4-bsp/blob/master/linux-rtk/arch/arm64/boot/dts/realtek/rtd129x/rtd-1296.dtsi#L116
> >>
> >>
> >>> Any suggestion is welcome.
> >>>
> >>> Thanks!
> >>
> >> 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.
>
> On closer inspection, that BSP kernel implements a whole hrtimer-based
> bodge in arm_pmu to apparently work around not having usable interrupts,
> so yeah, this isn't going to be usable, sorry.
>
> Robin.

Hi all!

Thanks for all suggestions and inspection, if we make sure it is a hardware
design blunder, then it is accpetable for me, I just need to make sure it
isn't the kernel's fault, if so that's will be our fault:)

Thanks.

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