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Re: [Qemu-devel] [PATCH 1/2] accel: allows to select the "best" accelera
From: |
Daniel P. Berrange |
Subject: |
Re: [Qemu-devel] [PATCH 1/2] accel: allows to select the "best" accelerator |
Date: |
Tue, 4 Oct 2016 14:31:14 +0100 |
User-agent: |
Mutt/1.7.0 (2016-08-17) |
On Tue, Oct 04, 2016 at 02:49:21PM +0200, Thomas Huth wrote:
> On 04.10.2016 14:41, Paolo Bonzini wrote:
> >
> >
> > On 04/10/2016 13:30, Laurent Vivier wrote:
> >> But sometime, user wants to use a real accelerator without knowing
> >> if he really can, with, for instance accel=kvm:tcg.
> >> In this case, and if the accelerator is not available we
> >> have a noisy "XXX accelerator not found".
> >>
> >> By allowing the user to ask the "best" accelerator for the given
> >> target, we can avoid this problem.
> >>
> >> This patch introduces a new parameter for the "accel" property, the
> >> "best" keyword.
> >>
> >> You can ask to use the best accelerator with "-M accel=best",
> >> or if you want to use your favorite accelerator and if it is not
> >> available, the best one, you can use, for instance
> >> "-M accel=kvm:best".
> >
> > I don't think there's a single definition of a "best" accelerator. For
> > example, some "-cpu" features may be available only with TCG. In that
> > case, "kvm:tcg" has a clear meaning ("kvm" if it exists, otherwise
> > "tcg") but "best" doesn't.
> >
> > I agree with Daniel that unit tests should use "tcg" exclusively, at
> > least as a default.
>
> Using only tcg has also some disadvantages: For some tests, it's
> interesting to know whether they also work properly with KVM (e.g.
> migration tests), and only using tcg by default slows down the "make
> check" quite a bit - which might become an issue now that we're adding
> more and more tests.
Which tests are you seeing a slow-down for ? make check-unit doesn't
show any difference and for 'make check-qtest' the difference was
negligible (1m47 for KVM vs 1m57 for TCG). We shouldn't be running
extensive guest workloads in unit tests, so I'd be surprised to see
a major hit in unit test time.
Regards,
Daniel
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- [Qemu-devel] [PATCH 0/2] introduce "accel=best", Laurent Vivier, 2016/10/04
- [Qemu-devel] [PATCH 1/2] accel: allows to select the "best" accelerator, Laurent Vivier, 2016/10/04
- Re: [Qemu-devel] [PATCH 1/2] accel: allows to select the "best" accelerator, Daniel P. Berrange, 2016/10/04
- Re: [Qemu-devel] [PATCH 1/2] accel: allows to select the "best" accelerator, Paolo Bonzini, 2016/10/04
- Re: [Qemu-devel] [PATCH 1/2] accel: allows to select the "best" accelerator, Thomas Huth, 2016/10/04
- Re: [Qemu-devel] [PATCH 1/2] accel: allows to select the "best" accelerator,
Daniel P. Berrange <=
- Re: [Qemu-devel] [PATCH 1/2] accel: allows to select the "best" accelerator, Thomas Huth, 2016/10/04
- Re: [Qemu-devel] [PATCH 1/2] accel: allows to select the "best" accelerator, Paolo Bonzini, 2016/10/04
- Re: [Qemu-devel] [PATCH 1/2] accel: allows to select the "best" accelerator, Michael S. Tsirkin, 2016/10/04
- Re: [Qemu-devel] [PATCH 1/2] accel: allows to select the "best" accelerator, Paolo Bonzini, 2016/10/05
- Re: [Qemu-devel] [PATCH 1/2] accel: allows to select the "best" accelerator, Thomas Huth, 2016/10/05
- Re: [Qemu-devel] [PATCH 1/2] accel: allows to select the "best" accelerator, Paolo Bonzini, 2016/10/05
[Qemu-devel] [PATCH 2/2] tests: use accel=best instead of accel=kvm:tcg, Laurent Vivier, 2016/10/04
Re: [Qemu-devel] [PATCH 0/2] introduce "accel=best", Laurent Vivier, 2016/10/04
Re: [Qemu-devel] [PATCH 0/2] introduce "accel=best", Andrew Jones, 2016/10/04