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

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Message-ID: <CABPqkBQhUCUOszQzBJZd_pwX-nLf6y=0X-+swPi0pE3ivRpVcg@mail.gmail.com>
Date:	Tue, 11 Feb 2014 12:04:23 +0100
From:	Stephane Eranian <eranian@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
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 12:02 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> 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?
>
But on x86, you can load directly from memory, you'd only have the
target reg for the load. Not enough.
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