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

From: Masami Hiramatsu
Date: Sun Jul 09 2017 - 20:18:54 EST

Hello Arun,

On Fri, 7 Jul 2017 16:06:40 -0700
Arun Kalyanasundaram <arunkaly@xxxxxxxxxx> 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@xxxxxxxxxx>