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 09:41:37 -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

On 6/12/15 8:42 AM, Liang, Kan wrote:
>
>>
>> On 6/11/15 12:47 PM, Andi Kleen wrote:
>>>> Can you elaborate on an example? I don't see how this can happen
>>>> reading a maps file. And it does not read maps for all threads only
>>>> thread group leaders.
>>>
>>> This is with a stress test case that generates lots of small mappings
>>> at very high speed and frees them again. So the maps file keeps
>>> changing faster than the proc reader can keep it and it can end up
>>> with a live lock.
>>
>> Can you pass it along? I'd like to see how the task_diag proposal handles it.
>>
>> https://github.com/dsahern/linux/commits/task_diag-wip
>
> Hi David,
>
> I tried the task_diag on my platform, but it shows error message when I
> run perf top. " Message handling failed: rc -1, errno 25".
> And it looks perf top failed to get maps information.

Not surprising; it's only half-baked. Can you try perf-record? So far 
that is the only one I have tested.

Also, while running that kernel you can build the test programs under 
tools/testing/selftests/task_diag/ and try task_diag_all. I am away from 
my dev box at the moment. As I recall you will want to try 
'task_diag_all o $pid' or 'task_diag_all a'

I take this to mean you don't want to share the test program? I am 
curious as to how other tools handle this use case.
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