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

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Date:	Mon, 28 Apr 2014 12:01:33 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	linux-kernel@...r.kernel.org,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	David Ahern <dsahern@...il.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

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 ;-)

> 
> 
> [SNIP]
> > @@ -168,8 +174,8 @@ int dso__data_fd(struct dso *dso, struct machine *machine)
> >  	};
> >  	int i = 0;
> >  
> > -	if (dso->binary_type != DSO_BINARY_TYPE__NOT_FOUND)
> > -		return open_dso(dso, machine);
> 
> Why did you remove this line?

that code reopens already openned (and closed) file.. 
instead I return (not closed) descriptor from previous open

thanks,
jirka
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