Re: [dpdk-dev] [PATCH v7 2/4] virtio: Introduce config RTE_VIRTIO_INC_VECTOR

[Thomas Monjalon <thomas.monjalon@6wind.com>]

2016-02-07 19:21, Santosh Shukla:
> - virtio_recv_pkts_vec and other virtio vector friend apis are written for
>   sse/avx instructions. For arm64 in particular, virtio vector implementation
>   does not exist(todo).
> 
> So virtio pmd driver wont build for targets like i686, arm64.  By making
> RTE_VIRTIO_INC_VECTOR=n, Driver can build for non-sse/avx targets and will work
> in non-vectored virtio mode.
> 
> Disabling RTE_VIRTIO_INC_VECTOR config for :
> 
> - i686 arch as i686 target config says:
>   config/defconfig_i686-native-linuxapp-gcc says "Vectorized PMD is not
>   supported on 32-bit".
> 
> - armv7/v8 arch.

Yes it can be useful to disable vector optimizations, but it should done
at runtime, not a compilation option. I know it is already wrongly configured
at compilation for other drivers, we should fix them.

Here, you want to avoid SSE/AVX code on ARM. So we should just add the
appropriate ifdefs. Adding a compilation option does not prevent from enabling
it on ARM or old x86 which do not support these instructions.

Please virtio maintainers, we need to fix this code. Thanks