luis.henrix@xxxxxxxxx wrote: > Hi, > > I have the following scenario: a legacy application with RT constraints > that needs to be replicated. Basically, I need to run several instances > of this application on a single multi-core box. However, this is not as > simple as it sounds because the application assumes several things such > as exclusive access to HW, etc. > > So, instead of re-designing the application to co-exist with different > instances, I was wondering whether this could be done using a lazy > approach: running each instance within a virtual machine. > > I have enough cores available so that I can actually dedicate 1 or more > cores to each VM, but the problem is: will the application still be able > to meet its RT requirements? What are those RT requirements (order of magnitude, hard/soft, ie. what may happen if some deadline is missed)? > I guess that, if two VMs share the same > core(s), meeting the deadlines will not be possible without having a > special scheduler on the VMs manager. But what about if all the VMs have > their own cores? > > Of course there is still the issue with the shared access to the HW, > but since this HW (Ethernet NICs) also have support for virtualisation, > I could create virtual NICs for each of the VM instances. For the tests Frank cited, I tried to avoid device emulation as far as possible because it can be a bottleneck in QEMU (i.e. also KVM), specifically if you go below the millisecond and there is other guest I/O running in parallel. Still, if that may hurt you, depends on your RT requirements. > > Any experiences/thoughts/links? Would preemptrt+Xen be able to do this? Xen uses QEMU (a variant of it) in Dom0 for device emulation. Moreover, you would have to merge Xen's Dom0 patches with Preempt-RT patches - well, challenging, I bet. > preemptrt+kvm? Other options? Preempt-RT + kvm will at least allow you to tweak a lot, benefit from ongoing optimizations of both projects, or maybe even apply some "dirty tricks" to the hypervisor. IMO, a good starting point unless your requirements are way off. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
