Re: [PATCH 2/2] perf record: Replace 'overwrite' by 'flightrecorder' for better naming

[Wangnan (F)]

On 2017/11/1 21:26, Liang, Kan wrote:
> > The meaning of perf record's "overwrite" option and many "overwrite" in
> > source code are not clear. In perf's code, the 'overwrite' has 2 meanings:
> >   1. Make ringbuffer readonly (perf_evlist__mmap_ex's argument).
> >   2. Set evsel's "backward" attribute (in apply_config_terms).
> >
> > perf record doesn't use meaning 1 at all, but have a overwrite option, its
> > real meaning is setting backward.
> I don't understand here.
> 'overwrite' has 2 meanings. perf record only support 1.
> It should be a bug, and need to be fixed.

Not a bug, but ambiguous.

Perf record doesn't need overwrite main channel (we have two channels:
evlist->mmap is main channel and evlist->backward_mmap is backward channel),
but some testcases require it, and your new patchset may require it.
'perf record --overwrite' doesn't set main channel overwrite. What it does
is moving all evsels to backward channel, and we can move some evsels back
to the main channel by /no-overwrite/ setting. This behavior is hard to
understand.

Thank you.