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

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Date:   Wed, 21 Nov 2018 07:45:28 +0000
From:   Song Liu <songliubraving@...com>
To:     lkml <linux-kernel@...r.kernel.org>
CC:     "acme@...nel.org" <acme@...nel.org>, Jiri Olsa <jolsa@...nel.org>,
        "Peter Zijlstra" <peterz@...radead.org>,
        "wangnan0@...wei.com" <wangnan0@...wei.com>,
        Kernel Team <Kernel-team@...com>
Subject: perf tools: remove option --tail-synthesize ? 

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.

Thoughts?

Thanks,
Song