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

[Santosh Shukla <sshukla@mvista.com>]

On Mon, Feb 8, 2016 at 2:55 AM, Thomas Monjalon
<thomas.monjalon@6wind.com> wrote:
> 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.
>

Can't we consider this separate topic. My intent is virtio works for arm.

> 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.
>

By disabling VIRTIO_INC_VEC, compiler wont build
virtio_recv_pkts_vec(), so wont generate SSE/AVX code. Adding ifdef
for other arch example arm, is next step. Vector instruction for arm
are not fully supported, Its a todolist (Pl. refer my early v1/2
cover-letter), We'll add that after virtio functionally works for arm.

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