linux-kernel - Re: [PATCH 05/12] perf top: Moving lost events warning to helpline

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Date:   Tue, 20 Nov 2018 20:33:00 +0900
From:   Namhyung Kim <namhyung@...nel.org>
To:     Jiri Olsa <jolsa@...nel.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        David Miller <davem@...emloft.net>, kernel-team@....com
Subject: Re: [PATCH 05/12] perf top: Moving lost events warning to helpline

On Tue, Nov 20, 2018 at 11:04:21AM +0900, Namhyung Kim wrote:
> On Mon, Nov 19, 2018 at 01:20:09PM +0100, Jiri Olsa wrote:
> > We can't display the UI box saying that we are slow in reader
> > thread. That will make perf top even slower and user even more
> > angry ;-)
> > 
> > Moving the UI box message out of the reader thread into UI thread
> > and changing it into helpline, so there's no 'press any key'
> > necessary.
> > 
> > Link: http://lkml.kernel.org/n/tip-0rpmmt3omlait889ewp1cl61@git.kernel.org
> > Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> > ---
> >  tools/perf/builtin-top.c | 16 +++++-----------
> >  1 file changed, 5 insertions(+), 11 deletions(-)
> > 
> > diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
> > index 047e99de09f3..1d77aa7650da 100644
> > --- a/tools/perf/builtin-top.c
> > +++ b/tools/perf/builtin-top.c
> > @@ -553,8 +553,6 @@ static void perf_top__sort_new_samples(void *arg)
> >  	struct perf_evsel *evsel = t->sym_evsel;
> >  	struct hists *hists;
> >  
> > -	perf_top__reset_sample_counters(t);
> > -
> >  	if (t->evlist->selected != NULL)
> >  		t->sym_evsel = t->evlist->selected;
> >  
> > @@ -571,6 +569,11 @@ static void perf_top__sort_new_samples(void *arg)
> >  
> >  	hists__collapse_resort(hists, NULL);
> >  	perf_evsel__output_resort(evsel, NULL);
> > +
> > +	if (t->lost)
> > +		ui_helpline__fpush("Too slow to read ring buffer (change period (-c/-F) or limit CPUs (-C)\n");
> 
> In general, ui_helpline__[f]push() requires corresponding __pop()
> which handles timeout logic (or something can dismiss the message).
> The ui_helpline__show() is to show the message and overwrite the old
> one.
> 
> But we don't use it strictly and I think just pr_err() or pr_warning()
> is ok here (which call ui_helpline__show() internally).
> 
> Anyway, I found that tui_helpline__push() should use ui__lock.
> Otherwise it could race with display thread and break rendering.
> A bug from the beginning but no one reported... :)

Hmm.. wait.  it caused a deadlock since it calls itself internally..
Will take a deeper look at it..

Thanks,
Namhyung