Mention incompatibility with perf 6

[Alizter]

Many issues here stem from perf 6 spitting out symbols magic-trace doesn't understand (yet). Since these will require a larger maintenance effort to fix, it might be worth mentioning that magic-trace only works with perf upto version 5.

[Xyene]

Please provide an example of the issue you are seeing. The major version in perf is not meaningful, and magic-trace is tested to work with 5.4-6.13 (but should also work with earlier versions). Any issues you are seeing are indeed bugs, but not expected ones where the solution would be to document an incompatibility; rather we'd want to fix the issues.

[Alizter]

Here for example:

$ perf --version
perf version 6.15.5

$ magic-trace run -- echo

[ perf record: Woken up 1 times to write data ]
[ Snapshot taken. ]
[ perf record: Captured and wrote 0.128 MB /tmp/magic_trace.tmp.bCT95C/perf.data ]
[ Finished recording. ]
[ Decoding, this takes a while... ]
(monitor.ml.Error
 ("BUG: exception raised while parsing perf output. Please report this to https://github.com/janestreet/magic-trace/issues/"
  (exn Not_found)
  (perf_output
   ("3315101/3315101 174106.015091592:          1                                 branches:u:   tr strt jmp                           0 [unknown] ([unknown]) =>     7f14f9e9c60b mprotect+0xb (/nix/store/q4wq65gl3r8fy746v9bbwgx4gzn0r2kl-glibc-2.40-66/lib/ld-linux-x86-64.so.2)")))
 ("Called from Base__Error.raise_s in file \"src/error.ml\", line 10, characters 26-47"
  "Called from Async_kernel__Pipe.map.(fun) in file \"src/pipe.ml\", line 1072, characters 65-70"
  "Caught by monitor Monitor.protect"))

but there are many other open tickets:

• BUG: exception raised while parsing perf output. #331
• "exception raised while parsing perf output" with "cbr: 36 freq: 3629 MHz (450%)" #324
• "exception raised while parsing perf output" with "branches:u: tr strt" #323
• Bug "(event_name cpu-clock)" #283

All with a common theme of being perf 6.x.

I don't expect these parsing issues to be fixed immediately and I understand there is a lack of resources for working on magic-trace at the moment.

I opened this issue just so that the issues with perf 6.x can be documented rather than leaving users scratching their heads. My own workaround was to simply get hold of perf 5.x from elsewhere.