Hi Masami,

I applied your patches and enabled your ptracingtest code. I noticed
that when there's dropped pages, the trace output is not in order:

 # trace-cmd start -B ptracingtest -e all -v -e '*lock*'
 # taskset -c 5 echo c > /proc/sysrq-trigger

On reboot, I ran:

 # trace-cmd show -B ptracingtest > /tmp/trace.out

Then executed the attached perl program:

  # ./read-ts.pl < /tmp/trace.out

And it errors our:

 30.212495 < 30.213534
           <...>-1048    [005] d....    30.212495: irq_enable: caller=irqentry_exit+0xf5/0x710 parent=0x0

That is, I think the zero timestamps may be messing with the order.

-- Steve