linux-kernel - Re: [PATCH 00/21] perf, c2c: Add new tool to analyze cacheline contention on NUMA systems

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Date:	Tue, 11 Feb 2014 12:02:42 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	Don Zickus <dzickus@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	LKML <linux-kernel@...r.kernel.org>,
	Jiri Olsa <jolsa@...hat.com>, Joe Mario <jmario@...hat.com>,
	Richard Fowles <fowles@...each.com>
Subject: Re: [PATCH 00/21] perf, c2c: Add new tool to analyze cacheline
 contention on NUMA systems

On Tue, Feb 11, 2014 at 11:58:45AM +0100, Stephane Eranian wrote:
> On Tue, Feb 11, 2014 at 11:52 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> > On Tue, Feb 11, 2014 at 11:35:45AM +0100, Stephane Eranian wrote:
> >> On Tue, Feb 11, 2014 at 8:14 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> >> >
> >> > That blows; how much is missing?
> >>
> >> They need to annotate load and stores. I asked for that feature a while ago.
> >> It will come.
> >
> > And there is no way to deduce the information? We have type information
> > for all arguments and local variables, right? So we can follow that.
> >
> > struct foo {
> >         int ponies;
> >         int moar_ponies;
> > };
> >
> > struct bar {
> >         int my_ponies;
> >         struct foo *foo;
> > };
> >
> > int moo(struct bar *bar)
> > {
> >         return bar->foo->moar_ponies;
> > }
> >
> > Since we have the argument type, we can find the type for both loads,
> > the first load:
> >
> >   *bar+8, we know is: struct foo * bar::foo
> >   *foo+4, we know is: int foo::moar_ponies
> >
> > Or am I missing something?
> 
> How do you know that load at addr 0x1000 is accessing variable bar?
> The IP gives you line number, and then what?
> I think dwarf has the mapping regs -> variable and yes, the type info.
> But I am not sure that's enough.

Ah, but if you have the instruction, you can decode it and obtain the
reg and thus type-info, no?

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