perf header: Why the HEADER_EVENT_DESC is needed?

Hi Stephane,

I wonder why we need to save the event descriptions in the feature area of file header. Since the perf_event_attr, its ids and the event name are already saved in the header, it seems a duplicate work to do that. For printing the information, we might reuse those info or evlist directly IMHO.

Am I missing something?

Thanks,
Namhyung

Unfortunately, I think you are.

There event names are not saved in header.c except indirectly by write_cmdline. But more importantly, event_desc makes it possible to connect an event name as passed on the cmdline with the corresponding attr struct.

Furthermore, it is also present in pipe mode, with the patch I posted months ago.

Finally, you cannot arbitrarily remove features like this. We do have tools that do
rely on the presence of EVENT_DESC.