Re: [RFC/PATCH 00/14] perf record: Add support to store data in directory

[Stephane Eranian]

On Mon, Feb 11, 2019 at 12:18 PM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
>
> On Mon, Feb 11, 2019 at 04:32:02PM -0300, Arnaldo Carvalho de Melo wrote:
> > Em Mon, Feb 11, 2019 at 07:53:06PM +0100, Jiri Olsa escreveu:
> > > On Mon, Feb 11, 2019 at 10:34:16AM -0800, Stephane Eranian wrote:
> > > > On Mon, Feb 11, 2019 at 2:20 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
> > > > > On Tue, Feb 05, 2019 at 02:37:27PM +0100, Jiri Olsa wrote:
> > > > > I think all could be added and worked around with exception
> > > > > of BUILD_ID, which we store at the end (after processing
> > > > > all data) and we need it early in the report phase
> >
> > > > Buildids are injected after the fact via perf inject when in pipe mode.
> >
> > > > > maybe it's time to re-think that buildid -> mmap event
> > > > > association again, because it's pain in current implementation
> > > > > as well
> >
> > > > Sure, but what do you propose?
> >
> > > this:
> > >
> > > > > looks like bpf code is actualy getting build ids and storing
> > > > > it for the callchains in kernel.. we can check if we can do
> > > > > something similar for mmap events
> >
> > kernel/bpf/stackmap.c
> >
> > /* Parse build ID from 64-bit ELF */
> > static int stack_map_get_build_id_64(void *page_addr,
> >                                      unsigned char *build_id)
> >
> > yeah, wasn't aware of that, good thing doing backports, huh? :-)
> >
> > So do you thing about having a PERF_SAMPLE_BUILDID in sample_type and go
> > and stash that thing in PERF_RECORD_MMAP2?
>
That would be special processing. Normally the sample_type go into
each RECORD_SAMPLE.
So I would not recommend this approach.

> I thought having new MMAP3 event version with buildid field in it
> if available and/or enabled by bit in perf_event_attr
>
I think MMAP3 is a cleaner approach, though it adds yet another MMAP event.

> jirka