Run RTLinux in a VM?

Run RTLinux in a VM?

[Vivek Ayer]

Hi all,

I'm building an application that requires the use of a real-time
kernel. I don't have money right now to purchase a physical machine to
run rtlinux on, and was going to try a virtual solution. Can I install
rtlinux in kvm, qemu, or uml?

Thanks,
Vivek

Re: Run RTLinux in a VM?

[Daniel James]

Hi Vivek,

> I don't have money right now to purchase a physical machine to
> run rtlinux on, and was going to try a virtual solution.

Personally, on a test machine I partition a hard disc into 10GB chunks
and put a distro in each partition. Then I don't have to worry about
possible side-effects of virtualisation on RT performance.

Cheers!

Daniel

Re: Run RTLinux in a VM?

[Klaas van Gend]

On Tuesday 03 August 2010 16:35:02 Vivek Ayer wrote:
> Hi all,
> 
> I'm building an application that requires the use of a real-time
> kernel. I don't have money right now to purchase a physical machine to
> run rtlinux on, and was going to try a virtual solution. Can I install
> rtlinux in kvm, qemu, or uml?

Yes, you can install it that way.

However, the effect would be similar to "upgrading" your speedometer in a car 
so the maximum speed is not 140 mph but 200 mph - the car won't go any faster!

So, if the platform isn't real time to start with, a real time kernel on top 
of that platform is not going to solve your problems.
The main kernel will happily block for indeterminate times at unexpected 
moments - your VM will only run outside of those blockages. 
Your VM's RT behavior will be worse than the original platform's.

-- 
Klaas van Gend
Senior Solutions Architect, MontaVista Software LLC

phone: +31 40 2801386

Re: Run RTLinux in a VM?

[Vivek Ayer]

Hi all,

Thanks for the quick responses. I'm not so concerned about the ill
effects of rt performance right this moment. I will probably get a
physical machine for it in two months or so. The main reason now is to
just get quick started on rt programming per say. My host machine is a
client written in PyQt that will be interfacing with RTLinux machine
and I just wanted to test a couple of things before I invested in a
rig for the RTLinux machine. I just want something that runs the RT
kernel for now.

The last time I tried with KVM, the rt kernel would panic on me while
loading some modules I suspect. So, if I'm going to use QEMU (No KVM),
running on a i386 host, running a i386 RTLinux guest, would I need to
apply any special patches to make sure the panic didn't occur.

See this thread for it hanging up in VMWare:
http://osdir.com/ml/linux.real-time.rtlinux.general/2004-11/msg00076.html

Apparently the rtl_time module causes the panic. Has this been taken
care of in the latest kernel?

Thanks,
Vivek

On Tue, Aug 3, 2010 at 7:35 AM, Vivek Ayer <vivek.ayer@gmail.com> wrote:
> Hi all,
>
> I'm building an application that requires the use of a real-time
> kernel. I don't have money right now to purchase a physical machine to
> run rtlinux on, and was going to try a virtual solution. Can I install
> rtlinux in kvm, qemu, or uml?
>
> Thanks,
> Vivek
>

Re: Run RTLinux in a VM?

[Vivek Ayer]

So you recommend I try a Linux 2.4 kernel instead? I wanted to see if
qemu could run 2.6, but if you recommend against that, then I'll try
2.4.

Can you attach your qemu config so I can try to clone you setup?

Thanks,
Vivek

On Tue, Aug 3, 2010 at 9:27 AM, Nicholas Mc Guire <der.herr@hofr.at> wrote:
> On Tue, 03 Aug 2010, Vivek Ayer wrote:
>
>> Hi all,
>>
>> Thanks for the quick responses. I'm not so concerned about the ill
>> effects of rt performance right this moment. I will probably get a
>> physical machine for it in two months or so. The main reason now is to
>> just get quick started on rt programming per say. My host machine is a
>> client written in PyQt that will be interfacing with RTLinux machine
>> and I just wanted to test a couple of things before I invested in a
>> rig for the RTLinux machine. I just want something that runs the RT
>> kernel for now.
>>
>> The last time I tried with KVM, the rt kernel would panic on me while
>> loading some modules I suspect. So, if I'm going to use QEMU (No KVM),
>> running on a i386 host, running a i386 RTLinux guest, would I need to
>> apply any special patches to make sure the panic didn't occur.
>>
>> See this thread for it hanging up in VMWare:
>> http://osdir.com/ml/linux.real-time.rtlinux.general/2004-11/msg00076.html
>>
>> Apparently the rtl_time module causes the panic. Has this been taken
>> care of in the latest kernel?
>>
> no this should not be necessary we have been running the 2.4.X RTLinux kernels
> on qemu for analysis purposes, as well as runing XtratuM (2.6.17,2.6.33) on
> qemu for debugging also - and functionally it seems to be ok - with timers
> set in the range of a few 10s of milliseconds it actually seems to run
> rt-tasks quite reliably at the functional level. RTLinux should not show
> any difference in behavior other than timing. If you use the rtl tracer you
> could see some strange results.
>
> hofrat
>

Re: Run RTLinux in a VM?

[Vivek Ayer]

Great! I appreciate it.

Thanks,
Vivek

On Tue, Aug 3, 2010 at 10:16 AM, Nicholas Mc Guire <der.herr@hofr.at> wrote:
> On Tue, 03 Aug 2010, Vivek Ayer wrote:
>
>> So you recommend I try a Linux 2.4 kernel instead? I wanted to see if
>> qemu could run 2.6, but if you recommend against that, then I'll try
>> 2.4.
>
> No that was not the intention - I just noted that I have tested 2.4 RTLinux
> and 2.6 XtratuM which is functionally so close to RTLinux that this
> indicates that unmodified RTLinux should also work - what RTLinux kernel/patch
> are you currently using ? send me that patch and I can give it a shot
> if you want with the setup here - should not take more than a few minutes.
>
>>
>> Can you attach your qemu config so I can try to clone you setup?
>>
>
> its 1 in the morning here now - will get you that tomrow - but actually
> its nothing specific - simply a default debian root-filesystems and a
> 2.6.33 kernel with xtratum patch applied. Anyway - will send you the
> exact commandline tomorow.
>
> later.
> hofrat
>

Re: Run RTLinux in a VM?

[Vivek Ayer]

Great. Will let you know if it works out in a couple of hours.

Thanks again,
Vivek

On Thu, Aug 5, 2010 at 8:03 AM, Nicholas Mc Guire <der.herr@hofr.at> wrote:
> On Tue, 03 Aug 2010, Vivek Ayer wrote:
>
>> Great! I appreciate it.
>>
>
> HI !
>
> took a bit longer - had to check up on a few things.
>
> qemu+gdb notes:
>
> host machine infomation:
> operation syetem: gentoo 64bits
> kernel version: 2.6.34-gentoo-r1
> cpu : amd64 x2
> qemu version: 0.11.1
>
> virtual machine infomation:
> config file: linux kernel 2.6.33.2 (attached)
> operation system in qemu: debian 5.0.3 32bits
> using net bridge and tap for network, network device is set to rtl8139
>
> qemu start arguments:
> #qemu -s -S -hda i386.img -kernel linux-2.6.33.2/arch/x86/boot/bzImage -append "root=/dev/hda1 console=ttyS0,115200 " -nographic -net nic,model=rtl8139 -net tap
>
> on host machine in directory linux-2.6.33.2/
> #gdb vmlinux
>
> du run within debugger.
>
> to run without debugger just remove the -s -S in the above commandline.
>
>
> HTH
> hofrat
>