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Subject: Re: [PATCH 2/3] perf tools: Cache dso data file descriptor
From: Namhyung Kim <namhyung@kernel.org>
To: Jiri Olsa <jolsa@redhat.com>
Cc: linux-kernel@vger.kernel.org, Corey Ashford <cjashfor@linux.vnet.ibm.com>,
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Date: Mon, 28 Apr 2014 22:16:34 +0900
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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;
	}


Thanks,
Namhyung