On Thu, Jul 25, 2024 at 10:56:05AM +0100, David Woodhouse wrote: > Hi Michael, thanks for the review! > > On Thu, 2024-07-25 at 01:48 -0400, Michael S. Tsirkin wrote: > > On Wed, Jul 24, 2024 at 06:16:37PM +0100, David Woodhouse wrote: > > > From: David Woodhouse <dwmw@xxxxxxxxxxxx> > > > > > > The vmclock "device" provides a shared memory region with precision clock > > > information. By using shared memory, it is safe across Live Migration. > > > > > > Like the KVM PTP clock, this can convert TSC-based cross timestamps into > > > KVM clock values. Unlike the KVM PTP clock, it does so only when such is > > > actually helpful. > > > > > > The memory region of the device is also exposed to userspace so it can be > > > read or memory mapped by application which need reliable notification of > > > clock disruptions. > > > > > > Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx> > > > --- > > > QEMU implementation at > > > https://git.infradead.org/users/dwmw2/qemu.git/shortlog/refs/heads/vmclock > > > > > > Although the ACPI device implemented in QEMU (and some other > > > hypervisor) stands alone, most of the fields and values herein are > > > aligned as much as possible with the nascent virtio-rtc specification, > > > with the intent that a version of the same structure can be > > > incorporated into that standard. > > > > Do you want to just help complete virtio-rtc then? Would be easier than > > trying to keep two specs in sync. > > The ACPI version is much more lightweight and doesn't take up a > valuable PCI slot#. (I know, you can do virtio without PCI but that's > complex in other ways). In general it shouldn't have to take up a PCI slot, that's just a common default policy. virtio-devices only need a dedicated slot if there's a need to do hotplug/unplug of them. There is a set of core devices for which hotplug doesn't make sense, which could all be put as functions in the same slot. ie virtio-rng, virtio-balloon and virtio-rtc, could all live in one slot. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
