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

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Date:	Fri, 12 Jun 2015 22:24:36 -0600
From:	David Ahern <dsahern@...il.com>
To:	"Liang, Kan" <kan.liang@...el.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?

David
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