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SubjectRe: [PATCH -tip 0/8] perf-probe updates

* Ingo Molnar <mingo@elte.hu> wrote:

> One hickup is that -d/--del does not appear to be working yet:
>
> # perf probe -l
> probe:schedule (on schedule)
>
> # perf probe -d probe:schedule
> Fatal: Failed to write event: Invalid argument

Ah, that was with an older kernel - a freshly booted kernel with
delete-probe syntax worked fine.

There's another small hickup i had - when i typoed 'perf probe -', it
gave me:

# perf probe -
No dwarf info found in the vmlinux - please rebuild with CONFIG_DEBUG_INFO.
An error occurred in debuginfo analysis. Try to use symbols.
Fatal: Failed to write event: Invalid argument

Similar thing happens if i try to probe a non-existent symbol:

# perf probe test
No dwarf info found in the vmlinux - please rebuild with CONFIG_DEBUG_INFO.
An error occurred in debuginfo analysis. Try to use symbols.
Fatal: Failed to write event: Invalid argument

I think we should print something more helpful, such as:

# perf probe test
Fatal: Kernel symbol 'test' not found - probe not added.

the debuginfo printout is not helpful in this case - we should fall back
to symbols silently, unless the nature of the error indicates that we
fail _because_ there's no debuginfo.

Here the failure was because the symbol does not exist.

There's similar problems in most other failure cases. Trying to remove a
non-existent probe gives:

# perf probe -d test
Warning: event "probe:test" is not found.

It should say something like:

# perf probe -d test
Info: event "probe:test" does not exist, could not remove it.

Also, it's possible to add multiple probes to the same function, using
'perf probe schedule' + 'perf probe schedule', etc. While in general it
makes sense to allow it, by default we should refuse the second,
identical probe on the symbol - and add a -f/--force option to force
duplicate probes. I.e. the second probe should print:

# perf probe schedule
Info: event "probe:schedule" already exists. (Use -f to force a duplicate.)

etc. Please try out various sensible and also less sensible options of
this tool and try to make it break - and see whether the behavior is
intuitive and obvious to users - whether the messages are consistent,
etc. etc.

Ingo


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