linux-kernel - Re: [PATCH 06/10] perf report: Setup browser if stdout is a pipe

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Date:	Tue, 06 Dec 2011 09:04:44 -0600
From:	Tom Zanussi <tzanussi@...il.com>
To:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Cc:	Robert Richter <robert.richter@....com>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Stephane Eranian <eranian@...gle.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 06/10] perf report: Setup browser if stdout is a pipe

On Tue, 2011-12-06 at 11:29 -0200, Arnaldo Carvalho de Melo wrote:
> Em Tue, Dec 06, 2011 at 11:32:36AM +0100, Robert Richter escreveu:
> > The decision to setup the browser should be made if stdout is pipe,
> > not stdin.
> 
> I can't remember what made that logic be like that...  Here it is:
> 
> commit 46656ac7fb3252f8a3db29b18638e0e8067849ba
> Author: Tom Zanussi <tzanussi@...il.com>
> Date:   Thu Apr 1 23:59:17 2010 -0500
> 
>     perf report: Introduce special handling for pipe input
>     
>     Adds special treatment for stdin - if the user specifies '-i -'
>     to perf report, the intent is that the event stream be written
>     to stdin rather than from a disk file.
>     
>     The actual handling of the '-' filename is done by the session;
>     this just adds a signal handler to stop reporting, and turns off
>     interference by the pager.
>     
>     Signed-off-by: Tom Zanussi <tzanussi@...il.com>
>     Acked-by: Thomas Gleixner <tglx@...utronix.de>
>     Cc: fweisbec@...il.com
>     Cc: rostedt@...dmis.org
>     Cc: k-keiichi@...jp.nec.com
>     Cc: acme@...stprotocols.net
>     LKML-Reference: <1270184365-8281-4-git-send-email-tzanussi@...il.com>
>     Signed-off-by: Ingo Molnar <mingo@...e.hu>
> 
> 
> I can't understand the comment either, as I think it should've read "the
> intent is that the event stream be _read from stdin_ rather than from a
> disk file."
> 
> And I don't know what would be the pager interference there.
> 
> Tom, could you elaborate on this?
> 

Hi Arnaldo,

Yeah, I think your comment is correct - the commit has a typo and should
read 'the intent is that the event stream be read from stdin'.

Basically, it's from the standpoint of a pipeline such as 'perf record |
perf report+scripting engine' where the output of perf record is
continuously fed into a scripting engine.  The script in then end takes
complete control of the output and doesn't want to be interfered with by
a pager.  IIRC that caused a problem with the 'top'-type scripts.

Anyway, from the standpoint of 'perf report' in a 'live' pipeline, I
think the current code is correct - if the input is coming from a pipe,
the assumption is that it's being passed to a script which will take
care of all the output details, so turn the pager off...

Tom 

> Thanks,
> 
> - Arnaldo
>     
>  
> > Signed-off-by: Robert Richter <robert.richter@....com>
> > ---
> >  tools/perf/builtin-report.c |    9 ++++++---
> >  1 files changed, 6 insertions(+), 3 deletions(-)
> > 
> > diff --git a/tools/perf/builtin-report.c b/tools/perf/builtin-report.c
> > index 4d7c834..88ca2d4 100644
> > --- a/tools/perf/builtin-report.c
> > +++ b/tools/perf/builtin-report.c
> > @@ -504,6 +504,8 @@ static const struct option options[] = {
> >  
> >  int cmd_report(int argc, const char **argv, const char *prefix __used)
> >  {
> > +	struct stat st;
> > +
> >  	argc = parse_options(argc, argv, options, report_usage, 0);
> >  
> >  	if (use_stdio)
> > @@ -514,10 +516,11 @@ int cmd_report(int argc, const char **argv, const char *prefix __used)
> >  	if (inverted_callchain)
> >  		callchain_param.order = ORDER_CALLER;
> >  
> > -	if (strcmp(input_name, "-") != 0)
> > -		setup_browser(true);
> > -	else
> > +	if (!fstat(STDOUT_FILENO, &st) && S_ISFIFO(st.st_mode))
> >  		use_browser = 0;
> > +	else
> > +		setup_browser(true);
> > +
> >  	/*
> >  	 * Only in the newt browser we are doing integrated annotation,
> >  	 * so don't allocate extra space that won't be used in the stdio
> > -- 
> > 1.7.7
> > 


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