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Subject: Re: problem with 'perf script -F weight'
To:     Jiri Olsa <jolsa@redhat.com>, Kan Liang <kan.liang@linux.intel.com>
Cc:     linux-perf-users@vger.kernel.org,
        Peter Zijlstra <peterz@infradead.org>,
        Joe Mario <jmario@redhat.com>,
        Jin Yao <yao.jin@linux.intel.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>
References: <YVNq9av/3Lwmom4T@krava>
From:   Andi Kleen <ak@linux.intel.com>
Message-ID: <5f182be7-1e6e-b864-66db-c5588601784a@linux.intel.com>
Date:   Tue, 28 Sep 2021 13:38:45 -0700
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On 9/28/2021 12:20 PM, Jiri Olsa wrote:
> hi,
> Joe reported broken -F weight in perf script with (on x86):
>
>    # ./perf mem record
>    # ./perf script -F weight
>    Samples for 'dummy:HG' event do not have WEIGHT attribute set. Cannot print 'weight' field.
>
> the problem seems to be introduced with the WEIGHT_STRUCT change:
>    ea8d0ed6eae3 perf tools: Support PERF_SAMPLE_WEIGHT_STRUCT
>
> which enables WEIGHT_STRUCT sample_type on x86 instead of WEIGHT,
> and leaves 'perf script -F weight' in the dark
>
> I'm not sure what the fix should look like.. should we allow user
> to use just 'WEIGHT' sample type? or is there a way to get original
> weight from 'WEIGHT_STRUCT' data, so we could fix just perf script?

We would need to support both in perf script, to handle both perf.data 
generated by old and new kernels on both big and little endian

So probably try one first and then the other while parsing

The same is true for all other users, so probably there needs to be a 
library function for this somewhere.

-Andi