I used to play with a realtime Linux system back in the 90s that had a sort of
virtualization architecture. It had a realtime executive that could run realtime tasks.
One of its tasks was the Linux kernel itself so this way the tasks could "talk"
with linux processes and make use of linux capabilities it lacked.
When I first worked with it, it ran the 1.3 kernel and it was really fast. A
6µsec latency. It got progressively worse with 2x kernels. But still much
better than the 150µsec quoted earler.
I can't remember what it was called. Somebody from New Mexico developed it.
There was also an offshoot development by a group in Italy.
On 08/27/2014 12:07 PM, Michael Duvall wrote:
Hello,
While I am thoroughly interested in SL topics, I rarely comment on threads.
Today is an exception. I work for a real-time linux vendor. I concur with
David Somerseth's summation. Real-time cannot be achieved under virtualization.
Regards,
--
*Michael Duvall*
Systems Analyst, Real-Time
michael.duv...@ccur.com <mailto:michael.duv...@ccur.com>
(954) 973-5395 direct
(954) 531-4538 mobile
CONCURRENT | 2881 Gateway Drive | Pompano Beach, FL 33069 | www.real-time.ccur.com
<http://www.real-time.ccur.com/>
-----Original Message-----
*From*: David Sommerseth <sl+us...@lists.topphemmelig.net
<mailto:david%20sommerseth%20%3csl+us...@lists.topphemmelig.net%3e>>
*Reply-to*: "scientific-linux-us...@listserv.fnal.gov"
<scientific-linux-us...@listserv.fnal.gov>
*To*: John Lauro <john.la...@covenanteyes.com
<mailto:john%20lauro%20%3cjohn.la...@covenanteyes.com%3e>>, Paul Robert Marino
<prmari...@gmail.com <mailto:paul%20robert%20marino%20%3cprmari...@gmail.com%3e>>
*Cc*: Brandon Vincent <brandon.vinc...@asu.edu <mailto:brandon%20vincent%20%3cbrandon.vinc...@asu.edu%3e>>,
llwa...@gmail.com <llwa...@gmail.com <mailto:%22llwa...@gmail.com%22%20%3cllwa...@gmail.com%3e>>,
SCIENTIFIC-LINUX-USERS@FNAL.GOV <scientific-linux-users@fnal.gov
<mailto:%22scientific-linux-us...@fnal.gov%22%20%3cscientific-linux-us...@fnal.gov%3e>>, Nico Kadel-Garcia
<nka...@gmail.com <mailto:nico%20kadel-garcia%20%3cnka...@gmail.com%3e>>
*Subject*: Re: about realtime system
*Date*: Wed, 27 Aug 2014 12:27:50 -0400
On 24/08/14 18:57, John Lauro wrote:
Why spread FUD about Vmware. Anyways, to hear what they say on the subject:
http://www.vmware.com/files/pdf/techpaper/latency-sensitive-perf-vsphere55.pdf
Anyways, KVM will not handle latency any better than Vmware.
You can currently not achieve true realtime characteristics when adding
virtualization, no matter the technology. The reason is that realtime
tasks must be able to preempt running tasks to be able to keep its
deadlines.
Consider running a virtualized realtime kernel running a realtime task,
on a host VM with a realtime kernel. When the task gets CPU time, it
preempts all other running tasks on the provided CPU core. But if the
VM host is not aware of this happening, it may just as well not give
enough runtime in the right time-window to the realtime guest OS. Thus
increasing the latency quite noticeably. So for this to work, the guest
OS kernel must be able to communicate to the host OS kernel that it has
a task which needs attention right now. And AFAIK, this mechanism is
not implemented anywhere.
I know there has been done some research on this topic some years ago,
and an interesting paper on it. But I don't know if this has come any
further.
<http://lwn.net/images/conf/rtlws11/papers/proc/p18.pdf>
