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

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Date:   Thu, 22 Nov 2018 18:18:15 +0000
From:   Song Liu <songliubraving@...com>
To:     "Wangnan (F)" <wangnan0@...wei.com>
CC:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        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 Nov 21, 2018, at 5:50 PM, Wangnan (F) <wangnan0@...wei.com> wrote:
> 
> 
> 
> 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?
> 

--overwrite implies --tail-synthesize. So with --overwrite, it is always
tail-synthesize. Do we really need --overwrite and --no-tail-synthesize? 
If not, we can probably just drop --tail-synthesize (or mark it as 
deprecated)? 

Thanks,
Song