Re: [Qemu-devel] [RFC PATCH v6 00/14] Reverse execution.

[Frederic Konrad <fred.konrad@greensocs.com>]

On 08/09/2014 09:57, Frederic Konrad wrote:
> On 01/09/2014 18:22, Paolo Bonzini wrote:
>> Il 03/07/2014 16:33, fred.konrad@greensocs.com ha scritto:
>>> From: KONRAD Frederic <fred.konrad@greensocs.com>
>>>
>>> Hi everybody,
>>>
>>> This is the sixth version of this RFC (see the changes below).
>>>
>>> Those are the two first patch-set we have been worked on for reverse 
>>> execution.
>>>
>>> The first part is fully reviewed except the "icount: introduce 
>>> icount timer"
>>> patch maybe we can merge them?
>>>
>>> The first series:
>>>    icount: put icount variables into TimerState.
>>>    migration: migrate icount fields.
>>>    migration: make qemu_savevm_state public.
>>>    icount: introduce icount timer.
>>>    icount: check for icount clock deadline when cpu loop exits.
>>>    icount: make icount extra computed on icount clock as well.
>>>    timer: add cpu_icount_to_ns function.
>>>
>>> are various preparation patches for reverse execution.
>>>
>>> The last patches:
>>>    trace-events: add reverse-execution events.
>>>    introduce reverse execution mechanism.
>>>    gdbstub: allow reverse execution in gdb stub.
>>>    cpu-exec: trigger a debug request when rexec stops.
>>>    rexec: synchronize icount on the next event.
>>>    rexec: allow to enable reverse execution.
>>>
>>> are reverse execution introduction.
>>>
>>> They can be clone at: git://git.greensocs.com/qemu_cexe.git:cexe_2_3_v6
>>>
>>> The third series will be sent as soon as possible and have some 
>>> issues with
>>> QEMU's thread as it use fork.
>>>
>>> This implementation of reverse execution works with instruction 
>>> counting:
>>>
>>> A new clock is implemented which is icount clock. It grows each time an
>>> instruction is executed and is totally independant of host clock.
>>>
>>> Snapshots are taken regularly (based on icount clock) with help of 
>>> migration
>>> code and written on the disk.
>>>
>>> When user wants to use reverse-stepi:
>>>   * Last snapshot is reloaded.
>>>   * A stop callback is created to be triggered at the previous 
>>> instruction.
>>>
>>> This stop callback generates a debug exception so QEMU stops in 
>>> debug mode.
>>>
>>> Command line:
>>>   * rexec suboption is added to icount to enable reverse execution, 
>>> it needs
>>>     icount=N and doesn't support auto mode.
>>>
>>> About non determinism in QEMU:
>>>   * This implementation doesn't take IO in account so any IO will 
>>> cause non
>>>     determinism and break reverse execution.
>>>
>>>   * The icount warp mechanism have been disabled when reverse 
>>> execution is
>>>     enabled so the time grow differently inside the VM.
>>>
>>> Testing:
>>>   * It has been tested on ARM without any IO such as network or 
>>> asynchronous file
>>>     access to keep the deterministic behaviour of icount.
>>>
>>> Known issues:
>>>   * On ARM stepi seems to do some additional steps which are added 
>>> to icount
>>>     counter so reverse-stepi just after stepi is broken.
>>>
>>>   * The IO replay explained above.
>> Hi, can you rebase and repost these patches?  It would be nice to have a
>> discussion of the different approaches to record/replay in your patches
>> and Pavel's (perhaps before Pavel presents at KVM Forum).
>>
>> Paolo
> Hi Paolo,
>
> Sorry for the delay.
> I'll rebase and resend these patches this week.
>
> Thanks,
> Fred
>
By the way how do you want to have this discussion?

At the KVM forum? Or by phone on KVM phone call?

Fred