Re: [PATCH 6/7] libperF: Add group support to perf_evsel__open

[Jiri Olsa <jolsa@redhat.com>]

On Wed, Jul 07, 2021 at 02:43:07PM -0300, Arnaldo Carvalho de Melo wrote:
> Em Tue, Jul 06, 2021 at 05:17:03PM +0200, Jiri Olsa escreveu:
> > Adding support to set group_fd in perf_evsel__open
> > call and make it to follow the group setup.
> > 
> > Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> > ---
> >  tools/lib/perf/evsel.c | 26 ++++++++++++++++++++++++--
> >  1 file changed, 24 insertions(+), 2 deletions(-)
> > 
> > diff --git a/tools/lib/perf/evsel.c b/tools/lib/perf/evsel.c
> > index 3e6638d27c45..9ebf7122d476 100644
> > --- a/tools/lib/perf/evsel.c
> > +++ b/tools/lib/perf/evsel.c
> > @@ -17,6 +17,7 @@
> >  #include <linux/string.h>
> >  #include <sys/ioctl.h>
> >  #include <sys/mman.h>
> > +#include <asm/bug.h>
> >  
> >  void perf_evsel__init(struct perf_evsel *evsel, struct perf_event_attr *attr,
> >  		      int idx)
> > @@ -76,6 +77,25 @@ sys_perf_event_open(struct perf_event_attr *attr,
> >  	return syscall(__NR_perf_event_open, attr, pid, cpu, group_fd, flags);
> >  }
> >  
> > +static int get_group_fd(struct perf_evsel *evsel, int cpu, int thread)
> > +{
> > +	struct perf_evsel *leader = evsel->leader;
> > +	int fd;
> > +
> > +	if (evsel == leader)
> > +		return -1;
> > +
> > +	/*
> > +	 * Leader must be already processed/open,
> > +	 * if not it's a bug.
> > +	 */
> > +	BUG_ON(!leader->fd);
> 
> Humm, having panics in library code looks ugly, why can't we just return
> some errno and let the whatever is using the library to fail gracefully?

true, I took it from perf code, did not realize this,
I'll check what can we do in ehre

> 
> I applied the patches so far, will make them available at tmp.perf/core
> now.

great, I'll take the patches from there for my next change

thanks,
jirka

> 
> - Arnaldo
> 
> > +	fd = FD(leader, cpu, thread);
> > +	BUG_ON(fd == -1);
> > +	return fd;
> > +}
> > +
> >  int perf_evsel__open(struct perf_evsel *evsel, struct perf_cpu_map *cpus,
> >  		     struct perf_thread_map *threads)
> >  {
> > @@ -111,11 +131,13 @@ int perf_evsel__open(struct perf_evsel *evsel, struct perf_cpu_map *cpus,
> >  
> >  	for (cpu = 0; cpu < cpus->nr; cpu++) {
> >  		for (thread = 0; thread < threads->nr; thread++) {
> > -			int fd;
> > +			int fd, group_fd;
> > +
> > +			group_fd = get_group_fd(evsel, cpu, thread);
> >  
> >  			fd = sys_perf_event_open(&evsel->attr,
> >  						 threads->map[thread].pid,
> > -						 cpus->map[cpu], -1, 0);
> > +						 cpus->map[cpu], group_fd, 0);
> >  
> >  			if (fd < 0)
> >  				return -errno;
> > -- 
> > 2.31.1
> > 
> 
> -- 
> 
> - Arnaldo
>