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From: Alejandro Lucero <alejandro.lucero@netronome.com>
To: dev <dev@dpdk.org>
Subject: [dpdk-dev] rte_eth_rx_queue_count accuracy
Date: Fri, 18 Sep 2015 11:33:36 +0100	[thread overview]
Message-ID: <CAD+H992XvC79Nwp5jHFZksC-egsDs413oShz=-Aq7AuOAsA2kw@mail.gmail.com> (raw)

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

             reply	other threads:[~2015-09-18 10:33 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-09-18 10:33 Alejandro Lucero [this message]
2015-09-21 22:41 ` Stephen Hemminger
2015-09-22 10:40   ` Alejandro Lucero

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