Re: [PATCH] replay: synchronize on every virtual timer callback

[Pavel Dovgalyuk <dovgaluk@ispras.ru>]

On 19.05.2020 11:11, Alex Bennée wrote:
> Pavel Dovgalyuk <dovgaluk@ispras.ru> writes:
>
>> On 18.05.2020 18:56, Alex Bennée wrote:
>>> Philippe Mathieu-Daudé <philmd@redhat.com> writes:
>>>
>>>> + Alex
>>>>
>>>> On 5/6/20 10:17 AM, Pavel Dovgalyuk wrote:
>>>>> Sometimes virtual timer callbacks depend on order
>>>>> of virtual timer processing and warping of virtual clock.
>>>>> Therefore every callback should be logged to make replay deterministic.
>>>>> This patch creates a checkpoint before every virtual timer callback.
>>>>> With these checkpoints virtual timers processing and clock warping
>>>>> events order is completely deterministic.
>>>>> Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>
>>>>> ---
>>>>>     util/qemu-timer.c |    5 +++++
>>>>>     1 file changed, 5 insertions(+)
>>>>> diff --git a/util/qemu-timer.c b/util/qemu-timer.c
>>>>> index d548d3c1ad..47833f338f 100644
>>>>> --- a/util/qemu-timer.c
>>>>> +++ b/util/qemu-timer.c
>>>>> @@ -588,6 +588,11 @@ bool timerlist_run_timers(QEMUTimerList *timer_list)
>>>>>             qemu_mutex_lock(&timer_list->active_timers_lock);
>>>>>               progress = true;
>>>>> +        /*
>>>>> +         * Callback may insert new checkpoints, therefore add new checkpoint
>>>>> +         * for the virtual timers.
>>>>> +         */
>>>>> +        need_replay_checkpoint = timer_list->clock->type == QEMU_CLOCK_VIRTUAL;
>>>>>         }
>>>>>         qemu_mutex_unlock(&timer_list->active_timers_lock);
>>> So the problem I have with this as with all the record/replay stuff I
>>> need want to review is it's very hard to see things in action. I added a
>>> *very* basic record/replay test to the aarch64 softmmu tests but they
>>> won't exercise any of this code because no timers get fired. I'm
>>> assuming the sort of tests that is really needed is something that not
>>> only causes QEMU_CLOCK_VIRTUAL timers to fire and trigger logged HW
>>> events and ensure that things don't get confused in the process.
>> I encounter most of the bugs in different OS boot scenarios.
>>
>> We also have internal tests that include some computational, disk, and
>> network interaction tasks.
>>
>> Is it possible to add a test like booting a "real" OS and replaying
>> it?
> Yes - for these bigger more complex setups we should use the acceptance
> tests that run under Avocado. See "make check-acceptance".

I've installed avocado and avocado-framework, but got the following error:

venv/bin/python: No module named avocado

>
>>> If I read up the file I just get more questions than answers. For
>>> example why do we release the qemu_timers lock before processing the
>>> replay event? Is it that the replay event could cause another timer to
>> We release the lock, because accessing the replay module may process
>> some events and add more timers.
> OK. I guess the adding of the timer is a side effect of processing the
> event rather than something that gets added directly?

Right.


Pavel Dovgalyuk