linux-kernel - Re: [PATCH v6 1/6] perf report: properly handle branch count in match

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Date:   Thu, 19 Oct 2017 06:55:19 -0700
From:   Andi Kleen <ak@...ux.intel.com>
To:     Milian Wolff <milian.wolff@...b.com>
Cc:     acme@...nel.org, jolsa@...nel.org, namhyung@...nel.org,
        Linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        David Ahern <dsahern@...il.com>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Yao Jin <yao.jin@...ux.intel.com>,
        Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
Subject: Re: [PATCH v6 1/6] perf report: properly handle branch count in
 match_chain

On Thu, Oct 19, 2017 at 12:59:14PM +0200, Milian Wolff wrote:
> On Donnerstag, 19. Oktober 2017 00:41:04 CEST Andi Kleen wrote:
> > Milian Wolff <milian.wolff@...b.com> writes:
> > > +static enum match_result match_address_dso(struct dso *left_dso, u64
> > > left_ip, +					   struct dso *right_dso, u64 right_ip)
> > > +{
> > > +	if (left_dso == right_dso && left_ip == right_ip)
> > > +		return MATCH_EQ;
> > > +	else if (left_ip < right_ip)
> > > +		return MATCH_LT;
> > > +	else
> > > +		return MATCH_GT;
> > > +}
> > 
> > So why does only the first case check the dso? Does it not matter
> > for the others?
> > 
> > Either should be checked by none or by all.
> 
> I don't see why it should be checked. It is only required to prevent two 
> addresses to be considered equal while they are not. So only the one check is 
> required, otherwise we return either LT or GT.

When the comparison is always in the same process (which I think
is not the case) just checking the addresses is sufficient. If they are not then you
always need to check the DSO and only compare inside the same DSO.

-Andi