linux-kernel - Re: tracing/kprobes: [Bug] Identical timestamps on two kprobes that are few instructions apart

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Message-Id: <20170710091845.5db494f938a1ab6c8e2b0259@kernel.org>
Date:   Mon, 10 Jul 2017 09:18:45 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Arun Kalyanasundaram <arunkaly@...gle.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>, mhiramat@...nel.org,
        linux-kernel@...r.kernel.org, mingo@...nel.org,
        David Carrillo-Cisneros <davidcc@...gle.com>
Subject: Re: tracing/kprobes: [Bug] Identical timestamps on two kprobes that
 are few instructions apart

Hello Arun,

On Fri, 7 Jul 2017 16:06:40 -0700
Arun Kalyanasundaram <arunkaly@...gle.com> wrote:

> Hi Steven,
> 
> Thank you very much for your reply. I am using kernel - v4.12-rc3.
> 
> I did something like this and see the issue:
> # trace-cmd record -e kprobes:s1 -e kprobes:s2 -- taskset -c 0 my_program
> # ./trace-cmd report -t --cpu 0
> 
> The issue is pretty intermittent and only happens when there are a lot
> of samples, and so "my_program" generates a few hundred threads. Any
> pointers on debugging this would be very helpful, or please let me
> know if you want me to collect any log messages.

Ok, so this happens with ftrace+trace-cmd too.
If you run it on x86-64, could you add "-C x86-tsc" and check still
it happens? If not, I guess it happens when it adjusts timestamp.

Thank you,

-- 
Masami Hiramatsu <mhiramat@...nel.org>