Re: [Qemu-devel] Running Qemu in discrete time/step by step

[Matt]

Within the context of a simulator, qemu runs with a limited set of
devices so that removes some indeterminism but not all I guess.

VMsimint boasts exact reproducibility because they control all
outputs/inputs. I tried to look into their patch but the patch is
empty and instead there seems to be the partial (full ?) tree of qemu
1.6.
I suspect this might be quite some work to port this to the latest
qemu. It's sad because I really like the approach :)
(qemu changes in the latest archive of
http://www.ikr.uni-stuttgart.de/Content/IKRSimLib/Download/)

I guess I will stick to DCE with the hope that qemu considers the
usecase and make it easier.

Cheers

2017-10-24 6:33 GMT+09:00 Nutaro, James J. <address@hidden>:
> I don't expect exact repeatability, but I haven't tested for it either. The 
> machinery that prevents repeatability with replay will probably have the same 
> effect in the adevs/qemu simulator.
>
> -----Original Message-----
> From: Matt [mailto:address@hidden
> Sent: Monday, October 23, 2017 5:38 AM
> To: Nutaro, James J.
> Cc: Emilio G. Cota; address@hidden; Hajime Tazaki
> Subject: Re: [Qemu-devel] Running Qemu in discrete time/step by step
>
> I did not know about Qemu's record/replay mode which is an interesting
> feature but unneeded if a  2nd qemu run with the same inputs generated
> the same outputs (as it's the case with DCE).
> @nutaro Thanks for the updated patch. I will have a look at adevs. On
> a related note https://github.com/qemu/qemu/blob/master/docs/replay.txt
> enumerates different sources of indeterminism
> ==
> Replaying of the execution of virtual machine is bound by sources of
> non-determinism. These are inputs from clock and peripheral devices,
> and QEMU thread scheduling. Thread scheduling affect on processing events
> from timers, asynchronous input-output, and bottom halves.
> ==
>
> Do you manage to achieve perfect reproducibility with adevs + qemu ?
> If yes, is there any publication describing how you achieve this ?
>
> Best regards
> matt
>
> 2017-10-21 0:02 GMT+09:00 Nutaro, James J. <address@hidden>:
>> Thanks for taking a look at the patch. The most recent version of the patch 
>> will also work with KVM if you need to speed things up. You can find it here:
>>
>> https://patchwork.kernel.org/patch/9960369/
>>
>> Somehow I messed up that post and it shows V8 when it should be V9.
>>
>> You can get the simulator that it works with at
>>
>> https://sourceforge.net/projects/adevs/
>>
>> If nothing else, this simulator would give you a blue print for integration 
>> with another tool.
>>
>> Jim
>>
>> -----Original Message-----
>> From: Emilio G. Cota [mailto:address@hidden
>> Sent: Thursday, October 19, 2017 4:54 PM
>> To: Matt
>> Cc: address@hidden; Hajime Tazaki; Nutaro, James J.
>> Subject: Re: [Qemu-devel] Running Qemu in discrete time/step by step
>>
>> On Thu, Oct 19, 2017 at 14:14:12 +0900, Matt wrote:
>> (snip)
>>> - VMSimint does nearly that, it runs Qemu in discrete time but
>>> interface it with a JAVA simulator
>>> http://www.ikr.uni-stuttgart.de/Content/Publications/Archive/We_SIMUTools_2014_40209.pdf
>>> (with the code http://www.ikr.uni-stuttgart.de/Content/IKRSimLib/Download/)
>>> - http://web.ornl.gov/~nutarojj/adevs/ does sthg similar too
>>
>> Nutaro's work to interface with QEMU has been posted on the list:
>>   https://patchwork.kernel.org/patch/9572497/
>> I'm Cc'ing him in case he's not subscribed to the list.
>>
>>
>>> My questions would be:
>>> 1/ do you know of any other related work ?
>>
>> Is QEMU's record/replay mode of any use to you? Note that as is the
>> case with Nutaro's patch, you'll need icount mode (i.e. single-core)
>> enabled.
>>
>>> 2/ I believe there is interest from the research side but would it be
>>> possible to merge either approach or a similar one (adevs patch
>>> doesn't seem too big ~500 lines), would that be of interest for the
>>> Qemu comminity too ?
>>> 3/ if yes to 2. How to proceed, which one would be favorite ? if no,
>>> what should be improved ? or would that be a definitive no ?
>>
>> I think the adevs approach is reasonable. The patch hasn't gotten much
>> attention I guess because not many people care about this feature.
>> But if you could review the patch and certify that it works for you
>> (i.e. it works with simulators other than adevs), that could only help
>> the patch getting in.
>>
>> That said, I make no merging decisions so take this as just my opinion.
>>
>> Cheers,
>>
>>                 Emilio
>>
>