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

["Alex Bennée" <alex.bennee@linaro.org>]

Pavel Dovgalyuk <dovgaluk@ispras.ru> writes:

> 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

Hmm make check-acceptance should automatically setup local copies of
avocado using virtualenv. You shouldn't need to install the system
version.

>
>>
>>>> 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


-- 
Alex Bennée