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

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Date:	Wed, 17 Jun 2015 17:19:49 +0000
From:	"Liang, Kan" <kan.liang@...el.com>
To:	David Ahern <dsahern@...il.com>,
	"acme@...nel.org" <acme@...nel.org>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Huang, Ying" <ying.huang@...el.com>,
	"andi@...stfloor.org" <andi@...stfloor.org>
Subject: RE: [PATCH V3 1/2] perf,tools: add time out to force stop proc map
 processing


> 
> 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.
> 

I only test 50ms on my platforms. For all platforms, any recommendation?

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

If we set the default to infinity, the user will get nothing when perf top
runs in our case. There will be no warning. How do they know that they
should change the time out limit?
So I still think we need a finite default value. The problem is what's the number. 

Thanks,
Kan

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