Re: [PATCH 12/14] perf ftrace: Use pager for displaying result

[Namhyung Kim <namhyung@kernel.org>]

On Wed, 24 Apr 2013 16:17:24 +0200, Jiri Olsa wrote:
> On Tue, Apr 23, 2013 at 05:31:10PM +0900, Namhyung Kim wrote:
>> From: Namhyung Kim <namhyung.kim@lge.com>
>> 
>> It's convenient to use pager when seeing many lines of result.
>> 
> for some reason I'm able to get any output for 'live' command only
> when using --no-pager option. I dont get any data for:
>
>   # ./perf ftrace live ls
>
>   not even ls output
>
> But sometime I dont even get ftrace output for:
>
>   # ./perf --no-pager ftrace live ls
>
>   just ls output
>
>
> I wonder there's some race with reading trace_pipe file,
> I haven't checked deeply yet..

It seems go_pipe in perf_evlist__prepare_workload() was closed due to
the pager process, so the workload ended up blocking indefinitely.

I guess other subcommands were not affected by this since record doesn't
use a pager, and show and report don't have a workload.

Does the patch below fix it?



diff --git a/tools/perf/builtin-ftrace.c b/tools/perf/builtin-ftrace.c
index 95f9a7fa3e04..3f3a684193e0 100644
--- a/tools/perf/builtin-ftrace.c
+++ b/tools/perf/builtin-ftrace.c
@@ -1486,12 +1486,12 @@ __cmd_ftrace_live(struct perf_ftrace *ftrace, int argc, const char **argv)
        if (!argc && perf_target__none(&ftrace->target))
                usage_with_options(live_usage, live_options);
 
+       setup_pager();
+
        ret = ftrace_setup(ftrace, argc, argv);
        if (ret < 0)
                return ret;
 
-       setup_pager();
-
        ret = do_ftrace_live(ftrace);
 
        ftrace_teardown(ftrace);