linux-kernel - Re: [PATCH V3 3/3] perf tools: Construct LBR call chain

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Message-ID: <20141118075539.GA27645@krava.brq.redhat.com>
Date:	Tue, 18 Nov 2014 08:55:39 +0100
From:	Jiri Olsa <jolsa@...hat.com>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	"Liang, Kan" <kan.liang@...el.com>,
	"acme@...nel.org" <acme@...nel.org>,
	"a.p.zijlstra@...llo.nl" <a.p.zijlstra@...llo.nl>,
	"eranian@...gle.com" <eranian@...gle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"paulus@...ba.org" <paulus@...ba.org>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>
Subject: Re: [PATCH V3 3/3] perf tools: Construct LBR call chain

On Tue, Nov 18, 2014 at 03:13:50PM +0900, Namhyung Kim wrote:

SNIP

> >> > +			 * in "from" register, while the callee is stored
> >> > +			 * in "to" register.
> >> > +			 * For example, there is a call stack
> >> > +			 * "A"->"B"->"C"->"D".
> >> > +			 * The LBR registers will recorde like
> >> > +			 * "C"->"D", "B"->"C", "A"->"B".
> >> > +			 * So only the first "to" register and all "from"
> >> > +			 * registers are needed to construct the whole
> >> stack.
> >> > +			 */
> >> 
> >> Andi is using some sanity checks:
> >> http://marc.info/?l=linux-kernel&m=141584447819894&w=2
> >> I guess this could be applied in here, once his patch gets in.
> >> 
> >
> > Are you suggesting me to remove the comments,
> > or rebase the whole patch to Andi's patch once it's merged?
> >
> > The branch history in Andi's patch is different as the call stack,
> > although they are both from LBR.
> > Andi's branch history recording branch records for
> > taken branches, interrupts, and exceptions.
> > While the LBR call stack records for the call stack.
> 
> Right.  And branch history can overlap with normal callchains so
> additional check in there is to remove duplication.  While LBR call
> stack is separated to user only so there should be no overlap.

hum, it seemed to me like the remove_loops function could be used
for this one as well.. but anyway I meant that this can be introduced
later after Andi's change gets in

thanks,
jirka
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