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

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Message-ID: <15CE7BE1-9D48-404D-BF09-847C09C4300E@fb.com>
Date:   Mon, 4 Mar 2019 21:40:07 +0000
From:   Song Liu <songliubraving@...com>
To:     Jiri Olsa <jolsa@...hat.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 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. 

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

Thanks,
Song