Re: [PATCH] ptp: Add vDSO-style vmclock support
From: Daniel P. Berrangé <hidden>
Date: 2024-07-25 11:32:02
Also in:
linux-arm-kernel, linux-rtc, lkml, qemu-devel, virtualization
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:quoted
On Wed, Jul 24, 2024 at 06:16:37PM +0100, David Woodhouse wrote:quoted
From: David Woodhouse <redacted> 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 <redacted> --- 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 :|