linux-kernel - [BUG] perf top: -z option does not work

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Date:	Tue, 12 Aug 2014 06:44:34 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Jiri Olsa <jolsa@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Namhyung Kim <namhyung@...nel.org>,
	"mingo@...e.hu" <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	David Ahern <dsahern@...il.com>
Subject: [BUG] perf top: -z option does not work

Hi,

My understanding is that the -z option is used to only print a profile
since the last refresh. So if I have a refresh of 5s, then it prints the profile
based on the samples accumulated over the last 5 seconds.

The Z mode used to be available interactively. Nowadays, it seems only
avail from the cmdline. But it does not work.

I run a simple test.
$ sudo perf top -z

Then for 5s I run a cycle-burning noploop program.
It shows up at the top. But when it terminates, the program  still stays
at the top of the profile for a long time. This is not what I'd expect.
The noploop line should disappear in the next couple of refreshes after
the program has terminated.

I am using tip.git and seeing the problem. But it seems, it's been there for a
long time.

Any idea what's wrong?

Thanks.
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