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Re: [PATCH] ptp: Add vDSO-style vmclock support
From: |
Michael S. Tsirkin |
Subject: |
Re: [PATCH] ptp: Add vDSO-style vmclock support |
Date: |
Fri, 26 Jul 2024 09:04:38 -0400 |
On Fri, Jul 26, 2024 at 02:00:25PM +0100, David Woodhouse wrote:
> On Fri, 2024-07-26 at 08:52 -0400, Michael S. Tsirkin wrote:
> > On Fri, Jul 26, 2024 at 09:35:51AM +0100, David Woodhouse wrote:
> > > But for this use case, we only need a memory region that the hypervisor
> > > can update. We don't need any of that complexity of gratuitously
> > > interrupting all the vCPUs just to ensure that none of them can be
> > > running userspace while one of them does an update for itself,
> > > potentially translating from one ABI to another. The hypervisor can
> > > just update the user-visible memory in place.
> >
> > Looks like then your userspace is hypervisor specific, and that's a
> > problem because it's a one way street - there is no way for hypervisor
> > to know what does userspace need, so no way for hypervisor to know which
> > information to provide. No real way to fix bugs.
>
> It's not hypervisor specific, but you're right that as it stands there
> is no negotiation of what userspace wants. So the hypervisor provides
> what it feels it can provide without significant overhead (which may or
> may not include the precise timekeeping, as discussed, but should
> always include the disruption signal which is the most important
> thing).
>
> The guest *does* know what the hypervisor provides. And when we get to
> do this in virtio, we get all the goodness of negotiation as well. The
> existence of the simple ACPI model doesn't hurt that at all.
Maybe it doesn't, at that. E.g. virtio does a copy, acpi doesn't?
I'll ponder compatibility over the weekend.
--
MST
- Re: [PATCH] ptp: Add vDSO-style vmclock support, (continued)
- Re: [PATCH] ptp: Add vDSO-style vmclock support, Michael S. Tsirkin, 2024/07/25
- Re: [PATCH] ptp: Add vDSO-style vmclock support, David Woodhouse, 2024/07/25
- Re: [PATCH] ptp: Add vDSO-style vmclock support, Michael S. Tsirkin, 2024/07/25
- Re: [PATCH] ptp: Add vDSO-style vmclock support, David Woodhouse, 2024/07/25
- Re: [PATCH] ptp: Add vDSO-style vmclock support, Michael S. Tsirkin, 2024/07/25
- Re: [PATCH] ptp: Add vDSO-style vmclock support, David Woodhouse, 2024/07/25
- Re: [PATCH] ptp: Add vDSO-style vmclock support, Michael S. Tsirkin, 2024/07/26
- Re: [PATCH] ptp: Add vDSO-style vmclock support, David Woodhouse, 2024/07/26
- Re: [PATCH] ptp: Add vDSO-style vmclock support, Michael S. Tsirkin, 2024/07/26
- Re: [PATCH] ptp: Add vDSO-style vmclock support, David Woodhouse, 2024/07/26
- Re: [PATCH] ptp: Add vDSO-style vmclock support,
Michael S. Tsirkin <=
- Re: [PATCH] ptp: Add vDSO-style vmclock support, David Woodhouse, 2024/07/26
- Re: [PATCH] ptp: Add vDSO-style vmclock support, Michael S. Tsirkin, 2024/07/26
- Re: [PATCH] ptp: Add vDSO-style vmclock support, Michael S. Tsirkin, 2024/07/26
- Re: [PATCH] ptp: Add vDSO-style vmclock support, David Woodhouse, 2024/07/26
- Re: [PATCH] ptp: Add vDSO-style vmclock support, Michael S. Tsirkin, 2024/07/26
- Re: [PATCH] ptp: Add vDSO-style vmclock support, David Woodhouse, 2024/07/26
- Re: [PATCH] ptp: Add vDSO-style vmclock support, Jonathan Cameron, 2024/07/26
- Re: [PATCH] ptp: Add vDSO-style vmclock support, David Woodhouse, 2024/07/26
- Re: [PATCH] ptp: Add vDSO-style vmclock support, Michael S. Tsirkin, 2024/07/28
- Re: [PATCH] ptp: Add vDSO-style vmclock support, David Woodhouse, 2024/07/28