From: "Alex Bennée" <alex.bennee@linaro.org>
To: Pavel Dovgalyuk <dovgaluk@ispras.ru>
Cc: pbonzini@redhat.com, "Pavel Dovgalyuk" <Pavel.Dovgaluk@gmail.com>,
"Philippe Mathieu-Daudé" <philmd@redhat.com>,
qemu-devel@nongnu.org, pavel.dovgaluk@ispras.ru
Subject: Re: [PATCH] replay: synchronize on every virtual timer callback
Date: Tue, 19 May 2020 09:11:14 +0100 [thread overview]
Message-ID: <87eergjqe5.fsf@linaro.org> (raw)
In-Reply-To: <b4da7577-8f42-3308-a4d6-05ff6451e944@ispras.ru>
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".
>> 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?
<snip>
--
Alex Bennée
next prev parent reply other threads:[~2020-05-19 8:13 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-06 8:17 [PATCH] replay: synchronize on every virtual timer callback Pavel Dovgalyuk
2020-05-18 10:58 ` Pavel Dovgalyuk
2020-05-18 11:24 ` Philippe Mathieu-Daudé
2020-05-18 15:56 ` Alex Bennée
2020-05-19 5:56 ` Pavel Dovgalyuk
2020-05-19 8:11 ` Alex Bennée [this message]
2020-05-19 10:21 ` Pavel Dovgalyuk
2020-05-19 10:32 ` Alex Bennée
2020-05-19 10:38 ` Pavel Dovgalyuk
2020-05-19 15:42 ` Philippe Mathieu-Daudé
2020-05-20 6:54 ` Pavel Dovgalyuk
2020-05-20 7:18 ` Philippe Mathieu-Daudé
2020-05-20 10:46 ` Pavel Dovgalyuk
2020-05-21 13:22 ` Paolo Bonzini
2020-05-22 6:39 ` Pavel Dovgalyuk
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