[PATCH 2/2] qemu: Generate command line for tb-cache feature

[Daniel P. Berrangé]

On Fri, Nov 05, 2021 at 09:28:16AM +0100, Michal Prívozník wrote:
> On 11/4/21 6:25 PM, Daniel P. Berrangé wrote:
> > On Thu, Nov 04, 2021 at 01:22:53PM +0100, Michal Privoznik wrote:
> >> Alright, here's the deal: to enable tb-cache one has to use
> >> '-accel tcg,tb-size=' which then conflicts with '-machine
> >> accel=tcg'. But sure, we can use the old -accel in this specific
> >> case. But because of how the tb-size argument is defined in QEMU
> >> there's no way for us to have a capability check. The feature was
> >> introduced in QEMU commit of v5.0.0-rc0~175^2~62 and is tied to
> >> TCG only. Therefore, I think we can live without capability
> >> check. Worst case scenario, QEMU fails to start.
> >>
> >> Resolves: https://gitlab.com/libvirt/libvirt/-/issues/229
> >> Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
> >> ---
> >>  src/qemu/qemu_command.c                       | 14 ++++++-
> >>  ...efault-cpu-tcg-features.x86_64-latest.args | 40 +++++++++++++++++++
> >>  tests/qemuxml2argvtest.c                      |  1 +
> >>  3 files changed, 54 insertions(+), 1 deletion(-)
> >>  create mode 100644 tests/qemuxml2argvdata/x86_64-default-cpu-tcg-features.x86_64-latest.args
> >>
> 
> 
> > IOW, long term we want to be using -accel exclusively.
> > 
> > Given our minimum QEMU 2.11.0, we can in fact use -accel
> > exclusively already AFAICT.
> > 
> > That would simplify this patch so that we're not supporting
> > distinct syntax with tb_cache.
> 
> Ah, I don't know why I thought the opposite. Let me post v2.

It is easily misunderstood, because QEMU does not makes it at all
clear which syntax is preferred, and its further confused by the
fact that they changed their mind & reversed the syntax sugaring :-)


Regards,
Daniel
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