Re: [PATCH v6 1/2] perf pmus: Sort/merge/aggregate PMUs like mrvl_ddr_pmu

[Robin Murphy <robin.murphy@arm.com>]

On 12/06/2024 1:32 pm, Ian Rogers wrote:
> On Wed, Jun 12, 2024 at 4:19 AM Aishwarya TCV <aishwarya.tcv@arm.com> wrote:
>>
>>
>>
>> On 15/05/2024 07:01, Ian Rogers wrote:
>>> The mrvl_ddr_pmu is uncore and has a hexadecimal address suffix while
>>> the previous PMU sorting/merging code assumes uncore PMU names start
>>> with uncore_ and have a decimal suffix. Because of the previous
>>> assumption it isn't possible to wildcard the mrvl_ddr_pmu.
>>>
>>> Modify pmu_name_len_no_suffix but also remove the suffix number out
>>> argument, this is because we don't know if a suffix number of say 100
>>> is in hexadecimal or decimal. As the only use of the suffix number is
>>> in comparisons, it is safe there to compare the values as hexadecimal.
>>> Modify perf_pmu__match_ignoring_suffix so that hexadecimal suffixes
>>> are ignored.
>>>
>>> Only allow hexadecimal suffixes to be greater than length 2 (ie 3 or
>>> more) so that S390's cpum_cf PMU doesn't lose its suffix.
>>>
>>> Change the return type of pmu_name_len_no_suffix to size_t to
>>> workaround GCC incorrectly determining the result could be negative.
>>>
>>> Signed-off-by: Ian Rogers <irogers@google.com>
>>> ---
>>>   tools/perf/util/pmu.c  | 33 +++++++++++++--------
>>>   tools/perf/util/pmus.c | 67 ++++++++++++++++++++++++------------------
>>>   tools/perf/util/pmus.h |  7 ++++-
>>>   3 files changed, 65 insertions(+), 42 deletions(-)
>>>
>>
>> Hi Ian,
>>
>> Perf test "perf_all_PMU_test" is failing when run against
>> next-master(next-20240612) kernel with Arm64 on JUNO in our CI. It looks
>> like it is failing when run on JUNO alone. Verified by running on other
>> boards like RB5 and Ampere_altra and confirming that it does not fail on
>> these boards. Suspecting that the suffixed 'armv8_pmuv3_0' naming could
>> be the reason of test failure.
>>
>> Reverting the change (3241d46f5f54) seems to fix it.
>>
>> This works fine on Linux version v6.10-rc3
>>
>> Failure log
>> ------------
>> 110: perf all PMU test:
>> --- start ---
>> test child forked, pid 8279
>> Testing armv8_pmuv3/br_immed_retired/
>> Event 'armv8_pmuv3/br_immed_retired/' not printed in:
>> # Running 'internals/synthesize' benchmark:
>> Computing performance of single threaded perf event synthesis by
>> synthesizing events on the perf process itself:
>>    Average synthesis took: 1169.431 usec (+- 0.144 usec)
>>    Average num. events: 35.000 (+- 0.000)
>>    Average time per event 33.412 usec
>>    Average data synthesis took: 1225.698 usec (+- 0.102 usec)
>>    Average num. events: 119.000 (+- 0.000)
>>    Average time per event 10.300 usec
>>
>>   Performance counter stats for 'perf bench internals synthesize':
>>
>>          3263664785      armv8_pmuv3_0/br_immed_retired/
>>
>>
>>        25.472854464 seconds time elapsed
>>
>>         8.004791000 seconds user
>>        17.060209000 seconds sys
>> ---- end(-1) ----
>> 110: perf all PMU test                                               :
>> FAILED!
> 
> Hi Aishwarya,
> 
> Thanks for reporting an issue. The test should be pretty self
> explanatory: it is doing a `perf stat -e
> armv8_pmuv3/br_immed_retired/` and then looking for that in the
> output. The event armv8_pmuv3/br_immed_retired/ comes from running
> perf list. As you can see in the output the event did work, so perf
> stat is working so nothing is actually broken here. What isn't working
> is the perf stat output matching the command line event and this is
> because of the unnecessary suffix on ARM's PMU name.
> 
> We have a problem that ARM have buggy PMU drivers, either from
> introducing new naming conventions or by just being broken:
> https://lore.kernel.org/lkml/CAP-5=fWNDkOpnYF=5v1aQkVDrDWsmw+zYX1pjS8hoiYVgZsRGA@mail.gmail.com/
> I've also asked that ARM step up their testing, for example in the
> event parsing testing the PMU is hardcoded to the x86 PMU name of
> 'cpu':
> https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/tests/parse-events.c?h=perf-tools-next#n2317
> On a cortex A53, then PMU is named 'armv8_cortex_a53':
> ```
> $ ls /sys/devices/armv8_cortex_a53/
> caps  cpus  events  format  perf_event_mux_interval_ms  power
> subsystem  type  uevent
> ```
> This name appears better, so what's up with ARM's core PMU name?

With Devicetree, we are able to derive a descriptive PMU name from the 
compatible string provided by the DT. Under ACPI, however, all we get 
told is whether each CPU has a usable PMU or not, so the best we can do 
is work out how many different CPU microarchitectures we have overall 
and create a PMU instance for each type. We still don't know *what* each 
one is, just that they're different, hence ending up with a common name 
plus a suffix which we can increment for disambiguation if and when we 
do see something new - userspace can still piece together the "cpus" 
lists and MIDRs to figure out what's what, we just can't do much in the 
kernel itself.

> Anyway, I'm tempted to fix this by just skipping the test on ARM given
> ARM's overall broken state.

This isn't a driver issue, it's a "the behaviour of 'perf list' changed 
inconsistently" issue. I also had a brief dig into this using a 
different arm64 ACPI system, and I think I can broadly characterise the 
cause. This is prior to 3241d46f5f54:

root@crazy-taxi:~# ./perf-mainline list armv8_pmuv3

List of pre-defined events (to be used in -e or -M):


armv8_pmuv3_0:
   L1-dcache-loads OR armv8_pmuv3_0/L1-dcache-loads/
   L1-dcache-load-misses OR armv8_pmuv3_0/L1-dcache-load-misses/
   L1-icache-loads OR armv8_pmuv3_0/L1-icache-loads/
   L1-icache-load-misses OR armv8_pmuv3_0/L1-icache-load-misses/
   dTLB-loads OR armv8_pmuv3_0/dTLB-loads/
   dTLB-load-misses OR armv8_pmuv3_0/dTLB-load-misses/
   iTLB-loads OR armv8_pmuv3_0/iTLB-loads/
   iTLB-load-misses OR armv8_pmuv3_0/iTLB-load-misses/
   branch-loads OR armv8_pmuv3_0/branch-loads/
   branch-load-misses OR armv8_pmuv3_0/branch-load-misses/
   l3d_cache_wb OR armv8_pmuv3_0/l3d_cache_wb/        [Kernel PMU event]


And this is after:

root@crazy-taxi:~# ./perf-next list armv8_pmuv3

List of pre-defined events (to be used in -e or -M):


armv8_pmuv3_0:
   L1-dcache-loads OR armv8_pmuv3_0/L1-dcache-loads/
   L1-dcache-load-misses OR armv8_pmuv3_0/L1-dcache-load-misses/
   L1-icache-loads OR armv8_pmuv3_0/L1-icache-loads/
   L1-icache-load-misses OR armv8_pmuv3_0/L1-icache-load-misses/
   dTLB-loads OR armv8_pmuv3_0/dTLB-loads/
   dTLB-load-misses OR armv8_pmuv3_0/dTLB-load-misses/
   iTLB-loads OR armv8_pmuv3_0/iTLB-loads/
   iTLB-load-misses OR armv8_pmuv3_0/iTLB-load-misses/
   branch-loads OR armv8_pmuv3_0/branch-loads/
   branch-load-misses OR armv8_pmuv3_0/branch-load-misses/
   l3d_cache_wb OR armv8_pmuv3/l3d_cache_wb/          [Kernel PMU event]

See the difference in the last line - it appears that CPU PMU events 
which map to common hardware/cache events *do* still report the full PMU 
name, but any PMU-type-specific events show a truncated name in list and 
thus fail the test's strict match against the full name reported by stat.

Thanks,
Robin.