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

[Richard Henderson <richard.henderson@linaro.org>]

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?


r~