Re: [Qemu-devel] time inside qemu

[Marius Monton <Marius.Monton@uab.cat>]

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That's true, and I don't care about it. I'd like to get a method to
stop/start time inside qemu in order to simulate execution of large
pieces of hw out of qemu (look at qemu-systemc project).
If qemu is freeze  meanwhile a systemc simulation is in progress
(simulating a HW device of system), time should be freeze also.
In this way, execution time of a program inside qemu should appear
shorter when using accelerator HW than only SW application. I know these
times are not reals, but it should be enough to estimate correctness and
execution time on real platforms.

Does a way to stop/start time inside qemu?

Thanks,

Màrius

En/na Paul Brook ha escrit:
> On Friday 29 December 2006 17:53, Màrius Montón wrote:
>   
>> Hi,
>>
>> As I understand, OSes running inside qemu "have" notion of time: (its
>> date and time works, time(1) command works, etc.).
>> My question is about how qemu manages time. I need to stop and start
>> again this "virtual-time".
>>     
>
> qemu doesn't maintain virtual time, it just uses the real host time.
>
>   
>> I just tried with cpu_disable_ticks() and cpu_enable_ticks(). It seems
>> to work partially: at least now system date and time are out of sync..
>>     
>
> I suspect you'll find that for anything other than very coarse user (ie. user 
> stop/continue) these are effectively useless.
>
> Any benchmark/performance measurements you make inside qemu are meaningless. 
> qemu performance bears no relation whatsoever to the performance 
> characteristics of real hardware.
>
>   

> Paul
>
>
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>
>   

-- 
Màrius Montón i Macián   marius.monton@uab.cat
<mailto:marius.monton@uab.cat>  http://cephis.uab.es
<http://www.mariusmonton.name>
Hardware Engineer
CEPHIS
Centre de Prototips i Solucions Hardware-Software
Dep. Microelectrònica i Sistemes Electrònics
ETSE - Universitat Autònoma de Barcelona (UAB) 	Phone: +34 935 813 534
Fax: +34 935 813 033
QC-2090D. ETSE. Campus UAB.
080193 Bellaterra



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