From: Jan Kiszka <[email protected]> Sent: Wednesday, February 4, 2026 10:38 PM > > On 05.02.26 06:42, Michael Kelley wrote: > > From: Jan Kiszka <[email protected]> Sent: Monday, February 2, 2026 > > 9:58 PM > >> > >> On 03.02.26 00:47, Long Li wrote: > >>>> From: Jan Kiszka <[email protected]> > >>>> > >>>> This resolves the follow splat and lock-up when running with PREEMPT_RT > >>>> enabled on Hyper-V: > >>> > >>> Hi Jan, > >>> > >>> It's interesting to know the use-case of running a RT kernel over Hyper-V. > >>> > >>> Can you give an example? > >>> > >> > >> - functional testing of an RT base image over Hyper-V > >> - re-use of a common RT base image, without exploiting RT properties > >> > >>> As far as I know, Hyper-V makes no RT guarantees of scheduling VPs for a > >>> VM. > >> > >> This is well understood and not our goal. We only need the kernel to run > >> correctly over Hyper-V with PREEMPT-RT enabled, and that is not the case > >> right now. > >> > >> Thanks, > >> Jan > >> > >> PS: Who had to idea to drop a virtual UART from Gen 2 VMs? Early boot > >> guest debugging is true fun now... > >> > > > > Hmmm. I often do printk()-based debugging via a virtual UART in a Gen 2 > > VM. The Linux serial console outputs to that virtual UART and I see the > > printk() output in PuTTY on the Windows host. What specifically are you > > trying to do? I'm trying to remember if there's any unique setup required > > on a Gen 2 VM vs. a Gen 1 VM, and nothing immediately comes to mind. > > Though maybe it's just so baked into my process that I don't remember it! > > > > Indeed: > > Powershell> Set-VMComPort -VMName "Debian 13" 1 \\.\pipe\comport > > <Start VM> > > Powershell> putty -serial \\.\pipe\comport > > Well hidden...
I just realized that the Hyper-V "Settings" UI for a VM shows COM1 and COM2 only for Gen1 VMs. I don't know why it's not shown for Gen2 VMs. The Powershell command you found is what I have always used. Michael
