Thanks, Steve.

Virtually, what I want is:

tracing_on(1), snapshort, traces..., snapshot, tracing_on(0).

If I understand right, I need the new feature "snapshot" in ftrace. But, it 
seems snapshot and ftrace are separated, which does not satisfy my need.

What is your suggestion?

Yuyang

-----Original Message-----
From: [email protected] 
[mailto:[email protected]] On Behalf Of Steven Rostedt
Sent: Thursday, September 12, 2013 11:38 AM
To: Du, Yuyang
Cc: [email protected]
Subject: Re: Query: is it possible to trace at exactly start and end time of 
tracing

On Thu, 12 Sep 2013 03:16:00 +0000
"Du, Yuyang" <[email protected]> wrote:

> Because I want to save start and end snapshots of some state.
> 

I'm not exactly sure what you want. You can use the new "snapshot"
feature (available since 3.10) and save the start and stop of a state without 
the need of tracing it.

echo 1 > /sys/kernel/debug/tracing/snapshot
cat /sys/kernel/debug/tracing/snapshot

-- Steve
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