Re: [PATCH v28 0/8] Timestamp synchronization of host - guest tracing session

[Steven Rostedt <rostedt@goodmis.org>]

On Tue, 09 Feb 2021 13:24:23 +0100
Dario Faggioli <dfaggioli@suse.com> wrote:
> 
> BTW, if I can pester you a little bit more, now that it works I'm
> trying to use this, and here's what I'm doing.
> 
> == VM:
> # echo tsc > /sys/devices/system/clocksource/clocksource0/current_clocksource
> # echo x86-tsc > /sys/kernel/tracing/trace_clock
> # trace-cmd agent
> 
> == Host:
> # echo x86-tsc > /sys/kernel/tracing/trace_clock
> # trace-cmd record -p nop -e sched:* -e kvm:* -e timer:hrtimer* -A tumbleweed-jeos:823 -e sched:* -e syscalls:*_clock_nanosleep -e timer:hrtimer* sleep 1
>

Note you can use -C x86-tsc on the command line which would handle the
clocks for you. I believe it may update the agent as well, but if not, you
can add it to the agent as well. Also "-p nop" shouldn't be needed, as that
would happen automatically if "-p" is left off.

 trace-cmd record -e sched -e kvm -e 'hrtimer*' -C x86-tsc \
   -A tumbleweed-jeos:823 -e sched -e '*_clock_nanosleep' -e 'hrtimer*' \
   sleep 1

should be equivalent. You may need to add '-C x86-tsc' after the -A, but I
think we made it match the host if a clock was supplied.
 
> And I do end up with the two files: trace.dat for the host and trace-
> (null).dat (oh, well :-D) for the guest.

I believe my latest push should fix that ;-)

-- Steve