From: "Daniel P. Berrangé" <berrange@redhat.com>
To: Thomas Huth <thuth@redhat.com>
Cc: "Kevin Wolf" <kwolf@redhat.com>,
qemu-block@nongnu.org, "Markus Armbruster" <armbru@redhat.com>,
"Wainer dos Santos Moschetta" <wainersm@redhat.com>,
qemu-devel@nongnu.org, "Paolo Bonzini" <pbonzini@redhat.com>,
"Max Reitz" <mreitz@redhat.com>,
"Philippe Mathieu-Daudé" <philmd@redhat.com>
Subject: Re: Priority of -accel (was: [PATCH] tests/qemu-iotests: Update tests to recent desugarized -accel option)
Date: Tue, 7 Jan 2020 14:26:09 +0000 [thread overview]
Message-ID: <20200107142609.GB3368802@redhat.com> (raw)
In-Reply-To: <3241dff4-6223-404f-55d4-846991763046@redhat.com>
On Tue, Jan 07, 2020 at 03:14:52PM +0100, Thomas Huth wrote:
> On 07/01/2020 13.54, Daniel P. Berrangé wrote:
> > On Tue, Jan 07, 2020 at 01:23:18PM +0100, Paolo Bonzini wrote:
> >> On 07/01/20 13:18, Thomas Huth wrote:
> >>> I don't think we need a separate priority parameter here. But IMHO it's
> >>> really rather common practice to prioritize the last option. So while
> >>> it might be more "self-explanatory" to a CLI newbie if the first
> >>> occurrence got the highest priority, it might be rather confusing
> >>> instead for a CLI veteran...?
> >>
> >> Prioritising the last certainly makes sense for a choose-one-only
> >> option, but I'm not sure it's the same for a choose-best option. After
> >> all it was -machine accel=kvm:tcg, not -machine accel=tcg:kvm...
> >
> > IIUC, the main use case for specifying multiple accelerators is
> > so that lazy invokations can ask for a hardware virt, but then get
> > fallback to TCG if not available. For things that should be platform
> > portabile, there's more than just kvm to consider though, as we have
> > many accelerators. Listing all possible accelerators is kind of
> > crazy though no matter what the syntax is.
> >
> > How about taking a completely different approach, inspired by the
> > -cpu arg and implement:
> >
> > -machine accel=best
>
> Something like that sounds like the best solution to me, but I'd maybe
> rather not call it "best", since the definition of "best" might depend
> on your use-case (e.g. do you want to use a CPU close to the host or
> something different which might be better emulated by TCG?).
>
> What about "-accel any" or "-accel fastest" or something similar?
If there are many HW virt accelerators on a host, "fastest" might
not be what we optimize for - we might prefer the more feature
complete one even if theoeretically slower.
I suggested "best" as it intentionally somewhat vague about what
particular criteria it optimizes for. I would document it as
"best: attempt to use a hardware virt accelerator for this
platform. Falls back to emulation if none is available
for use."
Utimately though this is just bikeshedding & I don't care much
about the specific name choice, just the general concept.
Regards,
Daniel
--
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next prev parent reply other threads:[~2020-01-07 14:27 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-06 13:09 [PATCH] tests/qemu-iotests: Update tests to recent desugarized -accel option Philippe Mathieu-Daudé
2020-01-06 13:16 ` Max Reitz
2020-01-07 10:03 ` Priority of -accel (was: [PATCH] tests/qemu-iotests: Update tests to recent desugarized -accel option) Thomas Huth
2020-01-07 10:14 ` Paolo Bonzini
2020-01-07 12:18 ` Thomas Huth
2020-01-07 12:23 ` Paolo Bonzini
2020-01-07 12:54 ` Daniel P. Berrangé
2020-01-07 14:14 ` Thomas Huth
2020-01-07 14:20 ` Priority of -accel Philippe Mathieu-Daudé
2020-01-07 14:27 ` Daniel P. Berrangé
2020-01-07 14:35 ` Thomas Huth
2020-01-13 14:39 ` Markus Armbruster
2020-01-13 16:14 ` Christophe de Dinechin
2020-01-13 16:23 ` Paolo Bonzini
2020-01-07 14:26 ` Daniel P. Berrangé [this message]
2020-01-08 10:39 ` Priority of -accel (was: [PATCH] tests/qemu-iotests: Update tests to recent desugarized -accel option) Alex Bennée
2020-01-08 10:58 ` Thomas Huth
2020-01-08 12:41 ` Paolo Bonzini
2020-01-08 13:10 ` Daniel P. Berrangé
2020-01-08 13:24 ` Paolo Bonzini
2020-01-08 14:00 ` Priority of -accel Thomas Huth
2020-01-08 11:00 ` Priority of -accel (was: [PATCH] tests/qemu-iotests: Update tests to recent desugarized -accel option) Peter Maydell
2020-01-10 10:43 ` Peter Maydell
2020-01-07 12:29 ` Kevin Wolf
2020-01-07 12:34 ` Priority of -accel Philippe Mathieu-Daudé
2020-01-07 12:37 ` Philippe Mathieu-Daudé
2020-01-07 13:55 ` Priority of -accel (was: [PATCH] tests/qemu-iotests: Update tests to recent desugarized -accel option) Christophe de Dinechin
2020-01-07 14:37 ` Paolo Bonzini
2020-01-07 14:42 ` Thomas Huth
2020-01-07 17:43 ` Christophe de Dinechin
2020-01-07 17:53 ` Peter Maydell
2020-01-08 9:47 ` Kevin Wolf
2020-01-13 16:17 ` Priority of -accel Markus Armbruster
2020-01-13 16:25 ` Paolo Bonzini
2020-01-14 8:59 ` Markus Armbruster
2020-01-14 10:44 ` Paolo Bonzini
2020-01-14 17:49 ` Christophe de Dinechin
2020-01-14 17:59 ` Daniel P. Berrangé
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