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

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Message-ID: <20140428133443.GE18628@krava.brq.redhat.com>
Date:	Mon, 28 Apr 2014 15:34:43 +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 Mon, Apr 28, 2014 at 10:16:34PM +0900, 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.
> 
> > 
> > > 
> > > 
> > > [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
> 
> But it'll overwrite the dso->binary_type then.  What about this?
> 
> 	if (dso->data_fd >= 0)
> 		return dso->data_fd;
> 
> 	if (dso->binary_type != DSO_BINARY_TYPE__NOT_FOUND) {
> 		dso->data_fd = open_dso(dso, machine);
> 		return dso->data_fd;
> 	}

right, makes sense.. I'll add it with the control code for the
number of openned descriptors

thanks,
jirka
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