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From:   Steve MacLean <Steve.MacLean@microsoft.com>
To:     Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>
CC:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@redhat.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Changbin Du <changbin.du@intel.com>,
        Eric Saint-Etienne <eric.saint.etienne@oracle.com>,
        John Keeping <john@metanate.com>,
        Andi Kleen <ak@linux.intel.com>,
        Song Liu <songliubraving@fb.com>,
        Davidlohr Bueso <dave@stgolabs.net>,
        Leo Yan <leo.yan@linaro.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Brian Robbins <brianrob@microsoft.com>,
        Tom McDonald <Thomas.McDonald@microsoft.com>,
        John Salem <josalem@microsoft.com>
Subject: RE: [PATCH] perf map: fix overlapped map handling
Thread-Topic: [PATCH] perf map: fix overlapped map handling
Thread-Index: AdVv5y6SzPv23L21QnSQJe3E6wWQgAAA9l0AAAMWwpABVHUWAAAUmtAQ
Date:   Sat, 28 Sep 2019 01:32:18 +0000
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>> An earlier version of this patch used:
>>   			after->start =3D map->end;
>> +			after->pgoff +=3D map->end - pos->start;
>>=20
>> Instead of the newer Functionally equivalent:
>>   			after->start =3D map->end;
>> +			after->pgoff =3D pos->map_ip(pos, map->end);
>>=20
>> I preferred the latter form as it made more sense with the assertion tha=
t the mapping of map->end should match in pos and after.
>
> So, if they are equivalent then I think its better to use code that resse=
mbles the kernel as much as possible, so that when in doubt we can compare =
the tools/perf calcs with how the kernel does it, filtering out things like=
 the PAGE_SHIFT, can we go that way?
>
> Also do you have some reproducer, if you have one then we can try and hav=
e this as a 'perf test' entry, bolting some more checks into tools/perf/tes=
ts/perf-record.c or using it as a start for a test that stresses this code.
>
> This is not a prerequisite for having your fix on, but would help checkin=
g that perf doesn't regresses in this area.
>
> - Arnaldo

I have updated the patch to use the earlier version, which more closely mat=
ches the kernel.

I have updated the commit message to include the repro info.

I am including a few other patches I have generated while adding support fo=
r perf jitdump to coreclr.