linux-kernel - Re: [PATCH] perf dso: Fix dso comparison

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Date:   Tue, 24 Mar 2020 18:07:23 +0530
From:   Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     acme@...nel.org, linux-kernel@...r.kernel.org, namhyung@...nel.org,
        mark.rutland@....com, naveen.n.rao@...ux.vnet.ibm.com,
        Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
Subject: Re: [PATCH] perf dso: Fix dso comparison



On 3/24/20 4:18 PM, Jiri Olsa wrote:
> On Tue, Mar 24, 2020 at 09:54:24AM +0530, Ravi Bangoria wrote:
>> Perf gets dso details from two different sources. 1st, from builid
>> headers in perf.data and 2nd from MMAP2 samples. Dso from buildid
>> header does not have dso_id detail. And dso from MMAP2 samples does
>> not have buildid information. If detail of the same dso is present
>> at both the places, filename is common.
>>
>> Previously, __dsos__findnew_link_by_longname_id() used to compare only
>> long or short names, but Commit 0e3149f86b99 ("perf dso: Move dso_id
>> from 'struct map' to 'struct dso'") also added a dso_id comparison.
>> Because of that, now perf is creating two different dso objects of the
>> same file, one from buildid header (with dso_id but without buildid)
>> and second from MMAP2 sample (with buildid but without dso_id).
>>
>> This is causing issues with archive, buildid-list etc subcommands. Fix
>> this by comparing dso_id only when it's present. And incase dso is
>> present in 'dsos' list without dso_id, inject dso_id detail as well.
>>
>> Before:
>>
>>    $ sudo ./perf buildid-list -H
>>    0000000000000000000000000000000000000000 /usr/bin/ls
>>    0000000000000000000000000000000000000000 /usr/lib64/ld-2.30.so
>>    0000000000000000000000000000000000000000 /usr/lib64/libc-2.30.so
>>
>>    $ ./perf archive
>>    perf archive: no build-ids found
>>
>> After:
>>
>>    $ ./perf buildid-list -H
>>    b6b1291d0cead046ed0fa5734037fa87a579adee /usr/bin/ls
>>    641f0c90cfa15779352f12c0ec3c7a2b2b6f41e8 /usr/lib64/ld-2.30.so
>>    675ace3ca07a0b863df01f461a7b0984c65c8b37 /usr/lib64/libc-2.30.so
>>
>>    $ ./perf archive
>>    Now please run:
>>
>>    $ tar xvf perf.data.tar.bz2 -C ~/.debug
>>
>>    wherever you need to run 'perf report' on.
>>
>> Reported-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>
> 
> looks good, do we need to add the dso_id check to sort__dso_cmp?

I guess with different filename there is no need to compare dso_id.
But for same filename, adding dso_id cmp will separate out the
samples:

Ex, Without dso_id compare:

   $ ./perf report -s dso,dso_size -v
     66.63%  /home/ravi/a.out                                  4096
     33.36%  /home/ravi/Workspace/linux/tools/perf/a.out       4096

   $ ./perf report -s dso,dso_size
     99.99%  a.out                 4096


With below diff:

   -       return strcmp(dso_name_l, dso_name_r);
   +       ret = strcmp(dso_name_l, dso_name_r);
   +       if (ret)
   +               return ret;
   +       else
   +               return dso__cmp_id(dso_l, dso_r);


   $ ./perf report -s dso,dso_size
     99.99%  a.out                 4096
     33.36%  a.out                 4096

though, the o/p also depends which other sort keys are used along
with dso key. Do you think this change makes sense?

Ravi