Re: The question about migration/checkpointing

[Alex Bennée]

Sergei Lyubski <slyubski@gmail.com> writes:

>   Hi guys,
>
> My name is Sergey. My company uses QEMU for  CPU performance 
> simulation/evaluaton.
> Sorry, I found  your emails in QEMU  relatively recent commits  into ram.c .  
> Why ram.c . Because I see some weirdness in
> the  behavior.
>   
> Our goal is :
>      a)  To boot  Linux , to launch some  TEST/SPEC, to drop a few 
> checkpoints.
>      b)  To resume  execution from  those checkpoints, to attach a 
> performance simulator and
>            to evaluate performance at the "hot" code  areas.
>
>   How we tried to do it .
>
>      a) run QEMU with -monitor telnet options
>      b) connect  to QEMU with telnet 
>      c)  after  LINUX  booted  in  QEMU monitor (telnet)  executed
>             migrate -d file://<FULL  CKPT PATH> 
>             quit
>       d)  run QEMU  with option -incoming file://<FULL CKPT PATH>
>
>   Now !!
>
>   If  I  drop the checkpoint  when running  on linux a long ( endless) test 
> which  prints on      the console,  everything works (!)
>  and  the console is properly restored.
>    
>   When I drop  the checkpoint  when the linux console is in shell  prompt, 
> the restoration does  not  work.
>    I see either error message  from  ram_load_precopy()
>        error_report("Unknown combination of migration flags: 0x%x",
>   flags);

I suspect seeing the value of flags will help with any diagnosis.

>
>        or
>
>    the console is locked, QEMU restarts and  runs  (ps, top).   The only  
> solution is to kill 
>    QEMU .  After that,  QEMU console is distorted and requires to type
>    RESET.

Are you able to attach with gdb and get a backtrace?

>
>     Could you please comment on the above issues. 
>     If you need more info I can send you my screen shots.
>     Please note that  that the similar behavior is observed on  both
>      qemu 9.0  ( stable-9.0)  and
>      qemu 8.x
>
> Thanks in advance.
> Sergey Lyubskiy

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro