linux-kernel - Re: perf tools: remove option --tail-synthesize ?

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Date:   Thu, 22 Nov 2018 09:50:15 +0800
From:   "Wangnan (F)" <wangnan0@...wei.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
CC:     Song Liu <songliubraving@...com>,
        lkml <linux-kernel@...r.kernel.org>,
        Jiri Olsa <jolsa@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Kernel Team" <Kernel-team@...com>
Subject: Re: perf tools: remove option --tail-synthesize ?



On 2018/11/21 21:11, Arnaldo Carvalho de Melo wrote:
> Em Wed, Nov 21, 2018 at 07:45:28AM +0000, Song Liu escreveu:
>> Hi,
>>
>> I found perf-record --tail-synthesize without --overwrite breaks symbols
>> for perf-script, perf-report, etc. For example:
>>
>> [root@]# ~/perf record -ag --tail-synthesize -- sleep 1
>> [ perf record: Woken up 1 times to write data ]
>> [ perf record: Captured and wrote 1.129 MB perf.data (3531 samples) ]
>> [root@]# ~/perf script | head
>> swapper     0 [000] 1250675.051971:          1 cycles:ppp:
>>         ffffffff81009e15 [unknown] ([unknown])
>>         ffffffff81196b19 [unknown] ([unknown])
>>         ffffffff81196579 [unknown] ([unknown])
>>         ffffffff81110ca7 [unknown] ([unknown])
>>         ffffffff81a01f4a [unknown] ([unknown])
>>         ffffffff81a017bf [unknown] ([unknown])
>>         ffffffff8180e17a [unknown] ([unknown])
>>
>> perf-record with --overwrite does NOT have this issue.
>>
>> After digging into this, I found this issue is introduced by commit
>> a73e24d240bc136619d382b1268f34d75c9d25ce.
>>
>> Reverting this commit does fix this issue. However, on a second thought,
>> I feel it is probably better just drop --tail-synthesize, as it doesn't
>> make much sense without --overwrite. All we need is to do tail_synthesize
>> when --overwrite is set.
>>

Some cases we use --overwrite without --tail-synthesize. How about setting
--tail-synthesize when selecting --overwrite by default, throw a warning
when --overwrite is not set and leave a --no-tail-synthesize option?

Thank you.

>> Thoughts?
> 
> Wang, wdyt?
> 
> - Arnaldo
>