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Re: [Qemu-devel] [PATCH v3 0/7] migration: pause-before-switchover
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] [PATCH v3 0/7] migration: pause-before-switchover |
Date: |
Thu, 19 Oct 2017 12:21:23 +0100 |
User-agent: |
Mutt/1.9.1 (2017-09-22) |
* Peter Xu (address@hidden) wrote:
> On Wed, Oct 18, 2017 at 06:40:06PM +0100, Dr. David Alan Gilbert (git) wrote:
>
> [...]
>
> > The precopy flow is:
> > active->pre-switchover->device->completed
> >
> > The postcopy flow is:
> > active->pre-switchover->postcopy-active->completed
>
> The naming is still slightly confusing to me:
>
> (1) we have a capability called "pause-before-switchover", so it feels
> like there is something called "switchover" and if we enable this
> we'll pause before that point;
>
> (2) we have a new status "pre-switchover", it feels like that's the
> point before we are in "switchover" state;
>
> (3) we don't really have a "switchover" state, but instead it's called
> "device" which is exactly the "switchover" action.
>
> Considering (1) and (2), I would prefer "device" state to be just
> "switchover"...
Yes I stuck to pause-before-device and device originally; but
what we're doing during the 'device' stage is mostly saving device
state; the actual switchover occurs at the end. So hmm.
> Further, not sure we can unify the state transition as well (say, we
> add this switchover state even without cap "pause-before-switchover"
> set, although it does not make much sense itself). Then, we can also
> unify the precopy/postcopy state machine into one:
>
> active->
> [pre-switchover->] (optional, decided by "pause-before-switchover")
> switchover->
> [postcopy-active->] (optional, decided by "postcopy-arm")
> completed
I didn't want to change the state transition behaviour without the
capability set, since that could upset an existing libvirt that would
get confused by the new state.
Dave
> (Sorry I am discussing the naming again instead of reviewing real
> stuff!)
>
> --
> Peter Xu
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK