Re: [PATCH v2 3/3] target/arm: Add sve-default-vector-length cpu property

[Andrew Jones <drjones@redhat.com>]

On Mon, Jul 26, 2021 at 08:33:52AM -1000, Richard Henderson wrote:
> On 7/26/21 4:59 AM, Andrew Jones wrote:
> > > +SVE User-mode Default Vector Length Property
> > > +--------------------------------------------
> > > +
> > > +For qemu-aarch64, the cpu property `sve-default-vector-length=N` is
> > > +defined to mirror the Linux kernel parameter file
> > > +`/proc/sys/abi/sve_default_vector_length`.  The default length, `N`,
> > > +is in units of bytes and must be between 16 and 8192.
> > 
> > Hmm. If a user inputs anything greater than 256, then won't it get
> > silently reduced to 256?
> 
> Yes.
> 
> > > +If not specified, the default vector length is 64.
> > > +
> > > +If the default length is larger than the maximum vector length enabled
> > > +with `sve<N>` properties, the actual vector length will be reduced.
> > 
> > Here it's pointed out that the default may be reduced, but it implies that
> > that only happens if an sve<N> property is also given. Won't users wonder
> > why they're only getting vectors that are 256 bytes large even when they
> > ask for more?
> 
> I guess adding that 256 is the maximum length supported by qemu should be sufficient?
>

Works for me.

Thanks,
drew