Messages in this thread | | | Date | Wed, 22 Nov 2023 15:49:18 +0000 | From | Mark Rutland <> | Subject | Re: [REGRESSION] Perf (userspace) broken on big.LITTLE systems since v6.5 |
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On Wed, Nov 22, 2023 at 10:06:23AM -0300, Arnaldo Carvalho de Melo wrote: > Em Wed, Nov 22, 2023 at 12:23:27PM +0900, Hector Martin escreveu: > > On 2023/11/22 1:38, Ian Rogers wrote: > > > On Tue, Nov 21, 2023 at 8:15 AM Mark Rutland <mark.rutland@arm.com> wrote: > > >> On Tue, Nov 21, 2023 at 08:09:37AM -0800, Ian Rogers wrote: > > >>> On Tue, Nov 21, 2023 at 8:03 AM Mark Rutland <mark.rutland@arm.com> wrote: > > >>>> On Tue, Nov 21, 2023 at 07:46:57AM -0800, Ian Rogers wrote: > > >>>>> On Tue, Nov 21, 2023 at 7:40 AM Mark Rutland <mark.rutland@arm.com> wrote: > > >>>>>> On Tue, Nov 21, 2023 at 03:24:25PM +0000, Marc Zyngier wrote: > > >>>>>>> On Tue, 21 Nov 2023 13:40:31 +0000, > > >>>>>>> Marc Zyngier <maz@kernel.org> wrote: > > >>>>>>>> > > >>>>>>>> [Adding key people on Cc] > > >>>>>>>> > > >>>>>>>> On Tue, 21 Nov 2023 12:08:48 +0000, > > >>>>>>>> Hector Martin <marcan@marcan.st> wrote: > > >>>>>>>>> > > >>>>>>>>> Perf broke on all Apple ARM64 systems (tested almost everything), and > > >>>>>>>>> according to maz also on Juno (so, probably all big.LITTLE) since v6.5. > > >>>>>>>> > > >>>>>>>> I can confirm that at least on 6.7-rc2, perf is pretty busted on any > > >>>>>>>> asymmetric ARM platform. It isn't clear what criteria is used to pick > > >>>>>>>> the PMU, but nothing works anymore. > > >>>>>>>> > > >>>>>>>> The saving grace in my case is that Debian still ships a 6.1 perftool > > >>>>>>>> package, but that's obviously not going to last. > > >>>>>>>> > > >>>>>>>> I'm happy to test potential fixes. > > >>>>>>> > > >>>>>>> At Mark's request, I've dumped a couple of perf (as of -rc2) runs with > > >>>>>>> -vvv. And it is quite entertaining (this is taskset to an 'icestorm' > > >>>>>>> CPU): > > >>>>>> > > >>>>>> IIUC the tool is doing the wrong thing here and overriding explicit > > >>>>>> ${pmu}/${event}/ events with PERF_TYPE_HARDWARE events rather than events using > > >>>>>> that ${pmu}'s type and event namespace. > > >>>>>> > > >>>>>> Regardless of the *new* ABI that allows PERF_TYPE_HARDWARE events to be > > >>>>>> targetted to a specific PMU, it's semantically wrong to rewrite events like > > >>>>>> this since ${pmu}/${event}/ is not necessarily equivalent to a similarly-named > > >>>>>> PERF_COUNT_HW_${EVENT}. > > >>>>> > > >>>>> If you name a PMU and an event then the event should only be opened on > > >>>>> that PMU, 100% agree. There's a bunch of output, but when the legacy > > >>>>> cycles event is opened it appears to be because it was explicitly > > >>>>> requested. > > >>>> > > >>>> I think you've missed that the named PMU events are being erreously transformed > > >>>> into PERF_TYPE_HARDWARE events. Look at the -vvv output, e.g. > > >>>> > > >>>> Opening: apple_firestorm_pmu/cycles/ > > >>>> ------------------------------------------------------------ > > >>>> perf_event_attr: > > >>>> type 0 (PERF_TYPE_HARDWARE) > > >>>> size 136 > > >>>> config 0 (PERF_COUNT_HW_CPU_CYCLES) > > >>>> sample_type IDENTIFIER > > >>>> read_format TOTAL_TIME_ENABLED|TOTAL_TIME_RUNNING > > >>>> disabled 1 > > >>>> inherit 1 > > >>>> enable_on_exec 1 > > >>>> exclude_guest 1 > > >>>> ------------------------------------------------------------ > > >>>> sys_perf_event_open: pid 1045843 cpu -1 group_fd -1 flags 0x8 = 4 > > >>>> > > >>>> ... which should not be PERF_TYPE_HARDWARE && PERF_COUNT_HW_CPU_CYCLES. > > >>>> > > >>>> Marc said that he bisected the issue down to commit: > > >>>> > > >>>> 5ea8f2ccffb23983 ("perf parse-events: Support hardware events as terms") > > >>>> > > >>>> ... so it looks like something is going wrong when the events are being parsed, > > >>>> e.g. losing the HW PMU information? > > >>> > > >>> Ok, I think I'm getting confused by other things. This looks like the issue. > > >>> > > >>> I think it may be working as intended, but not how you intended :-) If > > >>> a core PMU is listed and then a legacy event, the legacy event should > > The point is that "cycles" when prefixed with "pmu/" shouldn't be > considered "cycles" as HW/0, in that setting it is "cycles" for that > PMU.
Exactly.
> (but we only have "cpu_cycles" for at least the a53 and a72 PMUs I > have access in a Libre Computer rockchip 3399-pc hybrid board, if we use > it, then we get what we want/had before, see below):
Both Cortex-A53 and Cortex-A72 have the common PMUv3 events, so they have "cpu_cycles" and "bus_cycles".
The Apple PMUs that Hector and Marc anre using don't follow the PMUv3 architecture, and just have a "cycles" event.
[...]
> So what we need here seems to be to translate the generic term "cycles" > to "cpu_cycles" when a PMU is explicitely passed in the event name and > it doesn't have "cycles" and then just retry.
I'm not sure we need to map that.
My thinking is:
* If the user asks for "cycles" without a PMU name, that should use the PERF_TYPE_HARDWARE cycles event. The ARM PMUs handle that correctly when the event is directed to them.
* If the user asks for "${pmu}/cycles/", that should only use the "cycles" event in that PMU's namespace, not PERF_TYPE_HARDWARE.
* If we need a way so say "use the PERF_TYPE_HARDWARE cycles event on ${pmu}", then we should have a new syntax for that (e.g. as we have for raw events), e.g. it would be possible to have "pmu/hw:cycles/" or something like that.
That way there's no ambiguity.
Mark.
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