[dpdk-dev] rte_eth_rx_queue_count accuracy

[dpdk-dev] rte_eth_rx_queue_count accuracy

[Alejandro Lucero]

I have seen the API definition says nothing about accuracy but some PMD
implementations sacrifice accuracy for the sake of performance. If I'm not
understanding the code wrongly  i40e and ixgbe check DD bit just for the
first descriptor in a group of 4, and they take all of them as used if the
first descriptor is used.

By other hand, they do a "heavy" calculation when the descriptor ring wraps
which does not make sense (to me) if same performance goal is used.

There are PMDs not supporting this option and I can not see any app or
example using it so I do not know how important is this function, its
accuracy and its performance impact. Can someone comment on this?

Thanks

Re: [dpdk-dev] rte_eth_rx_queue_count accuracy

[Stephen Hemminger]

On Fri, 18 Sep 2015 11:33:36 +0100
Alejandro Lucero <alejandro.lucero@netronome.com> wrote:

> I have seen the API definition says nothing about accuracy but some PMD
> implementations sacrifice accuracy for the sake of performance. If I'm not
> understanding the code wrongly  i40e and ixgbe check DD bit just for the
> first descriptor in a group of 4, and they take all of them as used if the
> first descriptor is used.
> 
> By other hand, they do a "heavy" calculation when the descriptor ring wraps
> which does not make sense (to me) if same performance goal is used.
> 
> There are PMDs not supporting this option and I can not see any app or
> example using it so I do not know how important is this function, its
> accuracy and its performance impact. Can someone comment on this?
> 
> Thanks

I have version of this for virtio/vmxnet3
It is useful when using the interrupt control mode.

Re: [dpdk-dev] rte_eth_rx_queue_count accuracy

[Alejandro Lucero]

I can not see that code. Can you point out where is it?

Thanks

On Mon, Sep 21, 2015 at 11:41 PM, Stephen Hemminger <
stephen@networkplumber.org> wrote:

> On Fri, 18 Sep 2015 11:33:36 +0100
> Alejandro Lucero <alejandro.lucero@netronome.com> wrote:
>
> > I have seen the API definition says nothing about accuracy but some PMD
> > implementations sacrifice accuracy for the sake of performance. If I'm
> not
> > understanding the code wrongly  i40e and ixgbe check DD bit just for the
> > first descriptor in a group of 4, and they take all of them as used if
> the
> > first descriptor is used.
> >
> > By other hand, they do a "heavy" calculation when the descriptor ring
> wraps
> > which does not make sense (to me) if same performance goal is used.
> >
> > There are PMDs not supporting this option and I can not see any app or
> > example using it so I do not know how important is this function, its
> > accuracy and its performance impact. Can someone comment on this?
> >
> > Thanks
>
> I have version of this for virtio/vmxnet3
> It is useful when using the interrupt control mode.
>