linux-kernel - RE: [PATCH 1/1] perf,tools: add time out to force stop endless mmap processing

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Date:	Sat, 13 Jun 2015 15:06:31 +0000
From:	"Liang, Kan" <kan.liang@...el.com>
To:	David Ahern <dsahern@...il.com>, Andi Kleen <andi@...stfloor.org>
CC:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Huang, Ying" <ying.huang@...el.com>
Subject: RE: [PATCH 1/1] perf,tools: add time out to force stop endless mmap
 processing


> 
> coming back to this ...
> 
> On 6/12/15 2:39 PM, Liang, Kan wrote:
> >>> Yes, perf always can read proc file. The problem is that the proc
> >>> file is huge and keep growing faster than proc reader.
> >>> So perf top do loop in perf_event__synthesize_mmap_events until
> the
> >>> test case exit.
> >>
> >> I'm confused. How are you getting the above time to read /proc maps
> >> if it never finishes?
> >
> > I just tried to simplify the issue for perf record. So you may noticed
> > that I only read one thread. There are several threads in the system.
> > Also, I do the perf record test when starting the test case.
> > The proc file is not that big.
> > For perf top, it will monitor whole system. So it never finishes.
> 
> If the proc file is not that big for perf-record why is it a problem for perf-
> top? Both should only be reading the maps file for the thread group leader
> once and after it is processed getting MMAP events for changes.
> Why do you say perf-top can't handle it but perf-record can?

I once wanted to simplify the case. So I limited the perf record for one thread 
and sampled the test at very beginning. So we can see the processing time. 
But it makes things more complicate and confusing. :( 

Anyway, both system-wide-monitorings have this issue. The system-wide
monitorings include perf top and perf record -a.

Thanks,
Kan

> 
> David
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