Re: [dpdk-dev] [PATCH 1/3] ethdev: add max burst size to device info

["Ananyev, Konstantin" <konstantin.ananyev@intel.com>]

> -----Original Message-----
> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Matan Azrad
> Sent: Tuesday, December 12, 2017 10:46 AM
> To: Nikhil Agarwal <nikhil.agarwal@linaro.org>; dev@dpdk.org
> Cc: Hunt, David <david.hunt@intel.com>; nikhil.agarwal@nxp.com; hemant.agrawal@nxp.com; Yigit, Ferruh <ferruh.yigit@intel.com>
> Subject: Re: [dpdk-dev] [PATCH 1/3] ethdev: add max burst size to device info
> 
> Hi Nikhil
> 
> > -----Original Message-----
> > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Nikhil Agarwal
> > Sent: Tuesday, December 12, 2017 12:05 PM
> > To: dev@dpdk.org
> > Cc: david.hunt@intel.com; nikhil.agarwal@nxp.com;
> > hemant.agrawal@nxp.com; ferruh.yigit@intel.com
> > Subject: [dpdk-dev] [PATCH 1/3] ethdev: add max burst size to device info
> >
> > Currently, if the  rte_eth_rx_burst() function returns a value less than
> > *nb_pkts*, the application will assume that no more packets are present.
> >
> > Some of the hw queue based hardware can only support smaller burst for RX
> > and TX and thus break the expectation of the rx_burst API.
> >
> 
> Doesn't such like devices PMDs should try to retrieve multiple HW burst to adjust the asked received  packet number?

Same thought here...
Can't that limitation be hidden inside PMD by calling HW burst multiple times? 
Also if I am not mistaken - it would increase size of struct rte_eth_dev_info, right?
If so, then it means ABI breakage.
Konstantin

> 
> > This patch adds support to provide the maximum burst size that can be
> > supported by a given PMD. The dev_info is being memset to '0' in
> > rte_ethdev library. The value of '0' indicates that any value for burst size can
> > be supported i.e. no change for existing PMDs.
> >
> > The application can now use the lowest available max_burst_size value for
> > rte_eth_rx_burst.
> >
> 
> If you are talking about performance, maybe the right field to expose is something like "perf_burst_size" or "preferred_burst_size".
> I also suggest to expose different fields for RX and for TX.
> Maybe the rte_eth_rx\tx_burst() descriptions should be updated.
> 
> Thanks
> Matan.
> 
> > Signed-off-by: Nikhil Agarwal <nikhil.agarwal@linaro.org>
> > ---
> >  lib/librte_ether/rte_ethdev.h | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/lib/librte_ether/rte_ethdev.h b/lib/librte_ether/rte_ethdev.h
> > index 341c2d6..3ab6f02 100644
> > --- a/lib/librte_ether/rte_ethdev.h
> > +++ b/lib/librte_ether/rte_ethdev.h
> > @@ -1047,6 +1047,7 @@ struct rte_eth_dev_info {
> >  	/** Configured number of rx/tx queues */
> >  	uint16_t nb_rx_queues; /**< Number of RX queues. */
> >  	uint16_t nb_tx_queues; /**< Number of TX queues. */
> > +	uint16_t max_burst_size; /**< MAX burst size, 0 for no limit. */
> >  };
> >
> >  /**
> > --
> > 2.7.4