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

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Date:   Mon, 4 Mar 2019 14:52:24 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Song Liu <songliubraving@...com>
Cc:     Netdev <netdev@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "ast@...nel.org" <ast@...nel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        Kernel Team <Kernel-team@...com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "acme@...hat.com" <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 Wed, Feb 27, 2019 at 05:52:52PM +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:
> 
> I picked global sb_evlist and poll_thread because there 
> should be only one sb_evlist and one thread polling it. 
> There might be multiple evsel on the sb_evlist. 
> 
> I am not sure I understand your suggestion..
> 
> > struct perf_evlist {
> > 	...
> > 	struct {
> > 		pthread_t	th;
> > 		int		state;
> > 	} thread;
> 
> This will not be used by the main perf_evlist, right?

no, just by the thread interface

> 
> > };
> > 
> > typedef int (perf_evlist__thread_cb_t)(perf_evlist, union perf_event *event,....)
> 
> How do we use this callback? We need a way to specify which
> events to poll (mmap, bpf_event, ksymbol, etc). How do we do 
> that with the callback function?

you provide your own callback

jirka