Messages in this thread | | | Date | Tue, 21 Nov 2023 15:56:22 +0000 | From | Mark Rutland <> | Subject | Re: [REGRESSION] Perf (userspace) broken on big.LITTLE systems since v6.5 |
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On Tue, Nov 21, 2023 at 07:41:17AM -0800, Ian Rogers wrote: > Hi Marc,
Hi Ian,
> I'm unclear if you are running a newer perf tool on an older kernel or > not. In any case I'll assume the kernel and perf tool versions match. > In Linux 6.6 this patch was added to the ARM PMU: > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/perf/arm_pmu.c?id=5c816728651ae425954542fed64d21d40cb75a9f > > My guess is that the apple_icestorm_pmu requires a similar patch.
The apple_icestorm_pmu PMU driver uses the arm_pmu framework, so it's using that code (since v6.6).
> The perf tool is supposed to not use extended types when they aren't > supported: > https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/util/pmus.c?h=perf-tools-next#n532
How does that is_event_supported() check actually work? I suspect that's giving the wrong answer.
Regardless, I think the tool is doing something semantically wrong, see below.
> So I share your confusion as to why something broke. > > PERF_TYPE_HARDWARE is a legacy type where there are hardcoded type and > config values that correspond to an event. The PMU driver turns legacy > events into the real types. On BIG.little systems if the legacy events > are monitoring a task a different event is needed for each PMU (ie >1 > event). In your example you are monitoring 'ls', a task, and so > different cycles events are necessary. In the high 32-bits (the > extended type) the PMU is identified.
I think the interesting thing here is that the tool is mapping events with an explicit PMU into legacy PERF_TYPE_HARDWARE events, which is the opposite direction than intended. Regardless of whether PERF_TYPE_HARDWARE events can be targetted to a specific PMU, if the user has requested to use a specific PMU we should be using that PMU and related event namespace.
Marc's command line was:
sudo taskset -c 0 ./perf stat -vvv \ -e apple_icestorm_pmu/cycles/ \ -e apple_firestorm_pmu/cycles/ \ -e cycles \ ls
... and so the apple_*_pmu events should target their respective PMUs, and the plain 'cycles' event could legitimately be opened as a single PERF_TYPE_HARDWARE event, or split into two directed PERF_TYPE_HARDWARE events targetting the two PMUs.
However, thwe tool opens three (undirected?) PERF_TYPE_HARDWARE events:
Opening: apple_icestorm_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 = 3 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 Opening: 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 ------------------------------------------------------------
Mark.
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