Re: [PATCH v16 04/99] qtest/arm-cpu-features: Use generic qtest_has_accel() to check for KVM

[Eric Blake]

On Tue, Jun 08, 2021 at 02:39:03PM +0200, Philippe Mathieu-Daudé wrote:
> > 
> > Not enough coffee earlier. I think this is a documentation problem,
> > query-kvm returns a list of *runtime* accelerators:
> > https://www.mail-archive.com/qemu-devel@nongnu.org/msg811144.html
> > 
> > IIUC what Paolo said, if something asks for an accelerator that
> > is not present at build-time, then this is a configuration problem,
> > not relevant for the management interface.
> 
> Argh no... sigh. So we have 4 cases:
> 
> 1- accelerator not built
> 2- accelerator built in as module but not loaded
> 3- accelerator built in & loaded but not usable
> 4- accelerator built in & loaded and usable
> 
> QMP query-accels returns "accelerator built in & loaded"
> without precising it is usable.
> 
> qtest kvm_enabled() checks if the accelerator is enabled
> without checking it is built-in.
> 
> QMP query-kvm returns 'present' as in built-in (so case 1),
> and 'enabled' (a.k.a. 'allowed') updated once init_machine()
> succeeded (so case 4).
> 
> So, again, IIUC Paolo, what he said is for the management layer
> 1 and 2 are the same, the accelerator is not present.

Isn't 3 in the same boat?  Really, the management app cares if it can
use the accelerator, not whether it is present.

> 
> For qtests, we want the 'usable' case (4) right? Whether the
> accelerator is builtin / loaded is irrelevant.
> 
> Could we improve the terminology here? Maybe is_present() and
> is_usable()? Suggestions?
> 
> Do we need to add both query-present-accels query-usable-accels
> commands? Is it actually possible to return an array of 'usable'
> accelerators?
> 
> Maybe simply add query-present-accels() -> [] and
> query-usable-accel(accel) -> bool.

Can you just make query-accels return both pieces of information?

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
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