linux-kernel - Re: [PATCH 2/3] perf tools: Cache dso data file descriptor

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Date:	Tue, 29 Apr 2014 09:41:57 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	David Ahern <dsahern@...il.com>
Cc:	Jiri Olsa <jolsa@...hat.com>, linux-kernel@...r.kernel.org,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Jean Pihet <jean.pihet@...aro.org>
Subject: Re: [PATCH 2/3] perf tools: Cache dso data file descriptor

Hi David,

On Mon, 28 Apr 2014 08:57:49 -0600, David Ahern wrote:
> On 4/28/14, 7:16 AM, Namhyung Kim wrote:
>> 2014-04-28 (월), 12:01 +0200, Jiri Olsa:
>>> On Sun, Apr 27, 2014 at 11:36:35PM +0900, Namhyung Kim wrote:
>>>> 2014-04-17 (목), 19:39 +0200, Jiri Olsa:
>>>>> Keeping the data file description open for the whole life
>>>>> of the dso object.
>>>>
>>>> I suspect there might be an issue for reporting very large data file
>>>> with this approach - like open file limit?
>>>
>>> I've got as high as ~200 openned file descriptors for
>>> ~2GB data of system wide monitoring
>>>
>>> but right that could be an issue.. I wonder we could
>>> workaround this somehow, because the speed up is quite
>>> noticable
>>>
>>> how about we monitor number of openned dso file descriptor
>>> and once we cross this we close some portion of them
>>>
>>> or something along those lines ;-)
>>
>> Yeah, we'll need some way to control those eventually.
>
> Handle EMFILE failures. Find an "old" one and close it to let the new
> one succeed.

But it would make other open(), if any, fail anyway..  So I'd rather
limit the size of the dso cache to a reasonable size.

Thanks,
Namhyung
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