linux-kernel - Re: [PATCH v4 perf,bpf 14/15] perf: introduce side band thread

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Message-ID: <20190305110330.GA16022@krava>
Date:   Tue, 5 Mar 2019 12:03:30 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Song Liu <songliubraving@...com>
Cc:     Networking <netdev@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <Kernel-team@...com>,
        Peter Zijlstra <peterz@...radead.org>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        "jolsa@...nel.org" <jolsa@...nel.org>,
        "namhyung@...nel.org" <namhyung@...nel.org>
Subject: Re: [PATCH v4 perf,bpf 14/15] perf: introduce side band thread

On Mon, Mar 04, 2019 at 09:40:07PM +0000, Song Liu wrote:
> 
> 
> > On Feb 27, 2019, at 5:21 AM, Jiri Olsa <jolsa@...hat.com> wrote:
> > 
> > On Mon, Feb 25, 2019 at 04:20:18PM -0800, Song Liu wrote:
> > 
> > SNIP
> > 
> >> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
> >> index 8c902276d4b4..61b87c8111e6 100644
> >> --- a/tools/perf/util/evlist.c
> >> +++ b/tools/perf/util/evlist.c
> >> @@ -19,6 +19,7 @@
> >> #include "debug.h"
> >> #include "units.h"
> >> #include "asm/bug.h"
> >> +#include "bpf-event.h"
> >> #include <signal.h>
> >> #include <unistd.h>
> >> 
> >> @@ -1841,3 +1842,102 @@ struct perf_evsel *perf_evlist__reset_weak_group(struct perf_evlist *evsel_list,
> >> 	}
> >> 	return leader;
> >> }
> >> +
> >> +static struct perf_evlist *sb_evlist;
> >> +pthread_t poll_thread;
> > 
> > so some of the things are static and some like poll_args
> > you alloced on the stack.. I dont like this interface,
> > could we come up with something generic? perhaps
> > encapsulated in perf_evlist, like:
> > 
> > struct perf_evlist {
> > 	...
> > 	struct {
> > 		pthread_t	th;
> > 		int		state;
> > 	} thread;
> > };
> > 
> > typedef int (perf_evlist__thread_cb_t)(perf_evlist, union perf_event *event,....)
> > 
> > perf_evlist__start_thread(perf_evlist, perf_evlist__thread_cb_t cb);
> > perf_evlist__stop_thread(perf_evlist);
> > 
> > 
> > jirka
> 
> More questions on this proposal: 
> 
> IIUC, this approach creates one perf_evlist and one thread for each side band
> event (only bpf for now, more afterwards). Each of these perf_evlists will 
> create its own ring buffer. 
> 
> On the other hand, current patch allows different events to share the thread, 
> the perf_evlist, and the ring buffer. 

you can have those events in single evlist no?

> 
> If my understanding is correct, current patch would be more efficient down the 
> road? Did I miss some downsides of current patch?

I'd just like something configurable and with single handle
not scattered around the code, so it's easy to add new callback 

jirka