linux-kernel - Re: [PATCH V3 1/2] perf,tools: add time out to force stop proc map processing

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Message-ID: <20150617175302.GC3079@kernel.org>
Date:	Wed, 17 Jun 2015 14:53:02 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	David Ahern <dsahern@...il.com>
Cc:	kan.liang@...el.com, linux-kernel@...r.kernel.org,
	ying.huang@...el.com, andi@...stfloor.org
Subject: Re: [PATCH V3 1/2] perf,tools: add time out to force stop proc map
 processing

Em Wed, Jun 17, 2015 at 10:05:07AM -0600, David Ahern escreveu:
> On 6/17/15 1:56 AM, kan.liang@...el.com wrote:
> >diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
> >index 793b150..ac6cf2a 100644
> >--- a/tools/perf/util/event.c
> >+++ b/tools/perf/util/event.c
> >@@ -213,6 +213,8 @@ static int perf_event__synthesize_fork(struct perf_tool *tool,
> >  	return 0;
> >  }

> >+#define MMAP_TIMEOUT	(50 * 1000000ULL)

> How did you determine 50msec is a good time? This seems really low to me
> considering the range of platforms supported by perf and various run time
> conditions. The default needs to work right on all platforms.

> Why not have the default be infinity and users who need the feature use the
> option provided in patch 2?

Don't think that is a reasonable approach, how would be the workflow,
something like:

1) Fire up 'perf top'

2) Wait a long time.... maybe something is wrong, I guess I better
   exit, press Q, no response, ok, I think I'll kill this bugger

3) Read docs, etc, ah! That is it! --proc-map-timeout! How couldn't I
   think of that?

8-)

I think limiting this to say, half a second is ok, and the message about
the truncation happening surely suggests using --proc-map-timeout,
right?

Also please rename this MMAP_TIMEOUT define, this is not about a timeout
for a mmap operation, it is a timeout for parsing the proc mmap info,
i.e. something like:

#define PROC_MAP_PARSE_TIMEOUT  (50 * 1000000ULL)

Clarifies this and doesn't pollutes ctags like tools.

Thanks

- Arnaldo
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