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Date: Mon, 21 Sep 2015 15:41:30 -0700
From: Stephen Hemminger <stephen@networkplumber.org>
To: Alejandro Lucero <alejandro.lucero@netronome.com>
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Cc: dev <dev@dpdk.org>
Subject: Re: [dpdk-dev] rte_eth_rx_queue_count accuracy
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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.