linux-kernel - Re: [PATCHSET 00/17] perf report: Add -F option for specifying output fields (v4)

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Date:	Wed, 30 Apr 2014 09:35:55 -0400
From:	Don Zickus <dzickus@...hat.com>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Jiri Olsa <jolsa@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...nel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Namhyung Kim <namhyung.kim@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	David Ahern <dsahern@...il.com>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCHSET 00/17] perf report: Add -F option for specifying
 output fields (v4)

On Wed, Apr 30, 2014 at 08:38:10AM +0900, Namhyung Kim wrote:
> Hi Don,
> 
> On Tue, 29 Apr 2014 13:27:35 -0400, Don Zickus wrote:
> > On Tue, Apr 29, 2014 at 10:13:35AM +0900, Namhyung Kim wrote:
> >> >        /*
> >> >         * Addresses with no major/minor numbers are assumed to be
> >> >         * anonymous in userspace.  Sort those on pid then address.
> >> >         *
> >> >         * The kernel and non-zero major/minor mapped areas are
> >> >         * assumed to be unity mapped.  Sort those on address.
> >> >         */
> >> >
> >> >        if ((left->cpumode != PERF_RECORD_MISC_KERNEL) &&
> >> >            !l_map->maj && !l_map->min && !l_map->ino &&
> >> >            !l_map->ino_generation) {
> >> >                /* userspace anonymous */
> >> >
> >> >                if (left->thread->pid_ > right->thread->pid_) return -1;
> >> >                if (left->thread->pid_ < right->thread->pid_) return 1;
> >> 
> >> Isn't it necessary to check whether the address is in a same map in case
> >> of anon pages?  I mean the daddr.al_addr is a map-relative offset so it
> >> might have same value for different maps.
> >
> > That's why I sort on pids here.  Because the anon address might have the
> > same value for different maps.  The thought was to group all the pid
> > addresses together to keep things seperated.
> >
> > Do you see a different way to solve the problem?  I am not sure al_addr
> > vs. addr will make much difference here.
> 
> I'm not saying to get rid of the pid check, I'm saying that it might
> need to add another check for maps (i.e. start address) as there might
> be many maps in a single address space.

Hmm, I guess I would need to see an example.  While I agree there might be
many maps in a single address space (/proc/<pid>/maps demonstrates that),
I understood them to map to a unique location (ie no overlap) unless they
are shared.

I am willing to believe I missed scenario when sorting, I just can't think
of it (so I wouldn't know how to fix it).  That's why I was looking for an
example to make it more obvious to me.  Sorry for being slow..

Cheers,
Don
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