Re: [dpdk-dev] [PATCH v1] virtio: Use cpuflag for vector api

["Qiu, Michael" <michael.qiu@intel.com>]

On 3/2/2016 10:48 AM, Yuanhan Liu wrote:
> On Wed, Mar 02, 2016 at 02:10:14AM +0000, Qiu, Michael wrote:
>> On 3/1/2016 5:46 PM, Santosh Shukla wrote:
>>> On Tue, Mar 1, 2016 at 2:41 PM, Qiu, Michael <michael.qiu@intel.com> wrote:
>>>> On 2/26/2016 4:53 PM, Santosh Shukla wrote:
>>>>> Check cpuflag macro before using vectored api.
>>>>> -virtio_recv_pkts_vec() uses _sse3__ simd instruction for now so added cpuflag.
>>>>> - Also wrap other vectored freind api ie..
>>>>> 1) virtqueue_enqueue_recv_refill_simple
>>>>> 2) virtio_rxq_vec_setup
>>>>>
>>>>> todo:
>>>>> 1) Move virtio_recv_pkts_vec() implementation to
>>>>>    drivers/virtio/virtio_vec_<arch>.h file.
>>>>> 2) Remove use_simple_rxtx flag, so that virtio/virtio_vec_<arch>.h
>>>>>    files to provide vectored/non-vectored rx/tx apis.
>>>>>
>>>>> Signed-off-by: Santosh Shukla <sshukla@mvista.com>
>>>>> ---
>>>>> - v1: This is a rework of patch [1].
>>>>> Note: This patch will let non-x86 arch to use virtio pmd.
>>>>>
>>>>> [1] http://dpdk.org/dev/patchwork/patch/10429/
>>>>>
>>>>>  drivers/net/virtio/virtio_rxtx.c        |   16 +++++++++++++++-
>>>>>  drivers/net/virtio/virtio_rxtx.h        |    2 ++
>>>>>  drivers/net/virtio/virtio_rxtx_simple.c |   11 ++++++++++-
>>>>>  3 files changed, 27 insertions(+), 2 deletions(-)
>>>>>
>>>>> diff --git a/drivers/net/virtio/virtio_rxtx.c b/drivers/net/virtio/virtio_rxtx.c
>>>>> index 41a1366..ec0b8de 100644
>>>>> --- a/drivers/net/virtio/virtio_rxtx.c
>>>>> +++ b/drivers/net/virtio/virtio_rxtx.c
>>>>> @@ -67,7 +67,9 @@
>>>>>  #define VIRTIO_SIMPLE_FLAGS ((uint32_t)ETH_TXQ_FLAGS_NOMULTSEGS | \
>>>>>       ETH_TXQ_FLAGS_NOOFFLOADS)
>>>>>
>>>>> +#ifdef RTE_MACHINE_CPUFLAG_SSSE3
>>>>>  static int use_simple_rxtx;
>>>>> +#endif
>>>>>
>>>>>
>>>> I don't think so much #ifdef ... #endif in *.c file is a good choice.
>>>> Would you consider let it only in header file like:
>>>>
>>>> in drivers/net/virtio/virtio_rxtx.h
>>>>
>>>> [...]
>>>>
>>>> #ifdef RTE_MACHINE_CPUFLAG_SSSE3
>>>> int virtio_rxq_vec_setup(struct virtqueue *rxq);
>>>>
>>>> int virtqueue_enqueue_recv_refill_simple(struct virtqueue *vq,
>>>>         struct rte_mbuf *m);
>>>> #else
>>>> int virtio_rxq_vec_setup(__rte_unused struct virtqueue *rxq) {return -1;}
>>>> int virtqueue_enqueue_recv_refill_simple(__rte_unused struct virtqueue *vq,
>>>>                                          __rte_unused struct rte_mbuf *m) {
>>>>         return -1;
>>>> }
>>>> #endif
>>>>
>>>> and remove most #ifdef ... #endif in *.c file.
>>>>
>>> I guess, above approach wont work for non-x86 arch, ad those func are
>>> dummy, right? also code wont build for arm/non-86 arch because
>>> tx/rx_pkt_burst callback will be using x86 specific virtio vec rx/tx
>>> api.
>> You may right, but you really need to reduce the #ifdef in *.c files.
> In general, yes. But for this case, no: those vec stuff are for
> platforms that support it. For other platforms, we should not
> invoke a dummy function like virtio_rxq_vec_setup() at all.
>
> The right way to go is to add another wrapper beyond the vector
> stuff, something like:
>
> 	virtio_rxq_setup()
> 	{
>
> 		if (has_vec_support)
> 			virtio_rxq_vec_setup();
> 		else
> 			virtio_rxq_generic_setup();
> 	}

Actually, we could call vec first and if set up failed, fall back to
simple mode. Thus we could use dummy func, and it could make lift simple.

Thanks,
Michael
> Where virtio_rxq_vec_setup() could have a per-arch implementation,
> say for X86, or ARM.
>
> It touchs more code, but for now, I'd like to make it simple first.
> With the virtio_rxtx_simple.c isolated from Makefile, there aren't
> many #ifdef after all.
>
> 	--yliu
>