RFR: 7903740: JMH: Perf event validation not working with skid options [v4]

[Galder Zamarreño]

On Thu, 22 Aug 2024 12:54:10 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> Well, I would have expected we parsed `perf record` error and error code directly?
>> 
>> 
>> % perf record -e blah echo 1
>> event syntax error: 'blah'
>>                      ___ parser error
>> Run 'perf list' for a list of valid events
>> 
>>  Usage: perf record [<options>] [<command>]
>>     or: perf record [<options>] -- <command> [<options>]
>> 
>>     -e, --event <event>   event selector. use 'perf list' to list available events
>> 
>> % echo $?
>> 129
>> 
>> % perf record -e cycles:p echo 1 
>> Error:
>> cycles:p: PMU Hardware doesn't support sampling/overflow-interrupts. Try 'perf stat'
>> 
>> % echo $?                       
>> 255
>> 
>> % perf record -e cycles echo 1       
>> 1
>> [ perf record: Woken up 1 times to write data ]
>> [ perf record: Captured and wrote 0.013 MB perf.data (16 samples) ]
>> 
>> % echo $?                       
>> 0
>> 
>> 
>> Yes, I understand it actually does not test whether the counters _report_ non-zero values, but that's okay. We only do a light-weight validation that `perf record` even accepts these.
>
> Failing hard when some events cannot be supported is also proper, I'd think. So there is no need to verify them one by one. Keep it as simple as possible?

The thing is that `perf record` does not always fail when it doesn't work. For example in container ([example](https://github.com/galderz/github-actions/actions/runs/10723692355/job/29737549503)):


$ perf record --event cycles --output perf-record-validate.data echo 1
WARNING: Kernel address maps (/proc/{kallsyms,modules}) are restricted,
check /proc/sys/kernel/kptr_restrict and /proc/sys/kernel/perf_event_paranoid.

Samples in kernel functions may not be resolved if a suitable vmlinux
file is not found in the buildid cache or in the vmlinux path.

Samples in kernel modules won't be resolved at all.

If some relocation was applied (e.g. kexec) symbols may be misresolved
even with a suitable vmlinux or kallsyms file.

Couldn't record kernel reference relocation symbol
Symbol resolution may be skewed if relocation was used (e.g. kexec).
Check /proc/kallsyms permission or run as root.
1
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.001 MB perf-record-validate.data (3 samples) ]

$ echo $?
0

$ perf report -q -i perf-record-validate.data --stdio | grep cycles | wc -l
0


A lot of the issues I was having was because I assumed that in container `perf record` would fail but it doesn't, and later on you get errors saying that no events were recorded.

And in any case, if `perf record` fails, that's already handled by the current code when it calls `!failMsg.isEmpty()`.

> Failing hard when some events cannot be supported is also proper, I'd think. So there is no need to verify them one by one. Keep it as simple as possible?

I'll try to craft a command that checks all the events in one go and if any is missing fail hard.

-------------

PR Review Comment: https://git.openjdk.org/jmh/pull/132#discussion_r1745797969