Messages in this thread | | | From | Ian Rogers <> | Date | Tue, 21 Nov 2023 08:03:11 -0800 | Subject | Re: [REGRESSION] Perf (userspace) broken on big.LITTLE systems since v6.5 |
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On Tue, Nov 21, 2023 at 7:56 AM Mark Rutland <mark.rutland@arm.com> wrote: > > 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.
Maybe, the implementation is to check using perf_event_open: https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/util/print-events.c?h=perf-tools-next#n232
This is recycling logic from perf list where many legacy cache events are elided due to a lack of support.
> 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 \
-e cycles here is a direct request for the legacy cycles event. It will match in the parser here: https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/util/parse-events.l?h=perf-tools-next#n301
which goes to: https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/util/parse-events.y?h=perf-tools-next#n397
and as this is a hardware event there is wildcard expansion on each core PMU.
Thanks, Ian
> 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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