Re: [PATCH 1/4] perf trace: Improve error message when receive non-tracepoint events

[Wangnan (F)]

On 2016/4/8 23:22, Arnaldo Carvalho de Melo wrote:
> Em Fri, Apr 08, 2016 at 03:07:22PM +0000, Wang Nan escreveu:
> > Before this patch, strange error message is provided if passed a
> > non-tracepoint event to 'perf trace':
> >
> >   # perf trace -a  --ev cycles sleep 1
> >   Failed to set filter "common_pid != 27500" on event cycles with 22 (Invalid argument)
> >
> > This is because 'perf trace' accepts all valid events during cmdline
> > parsing, but in fact user can only provide tracepoints, because it
> > needs filter.
> >
> > This patch validate evlist, report error earlier:
> >
> >   # ./perf trace -a  --ev cycles sleep 1
> >   Only support tracepoint events!
> Humm, perhaps we should instead refrain from setting filters to non
> tracepoint events? I.e. I don't see why we whouldn't support, say,
> software events...
>
> /me trying some now, i.e.:
>
>    # trace --ev minor-faults --no-syscalls
>
> But it has some issues...
>
> - Arnaldo
>   

We already have commit fdf14720fbd02 ("perf tools: Only set filter for
tracepoints events") so you won't see the ugly error message again.

However, I think parsing non-tracepoint events in 'perf trace' is still
a challange. We never support it in 'perf trace' and I'm not too much
sure who will need this feature and how to use them, and why he/she can't
use 'perf record' instead.

Thank you.