[EXT] Re: [PATCH v5 2/2] app/testpmd: add command to process Rx metadata negotiation

[Hanumanth Reddy Pothula]

++ Ivan Malov and Andrew Rybchenko

> -----Original Message-----
> From: Ferruh Yigit <ferruh.yigit at amd.com>
> Sent: Tuesday, January 24, 2023 11:34 PM
> To: Hanumanth Reddy Pothula <hpothula at marvell.com>; Aman Singh
> <aman.deep.singh at intel.com>; Yuying Zhang <yuying.zhang at intel.com>
> Cc: dev at dpdk.org; andrew.rybchenko at oktetlabs.ru;
> viacheslavo at nvidia.com; Jerin Jacob Kollanukkaran <jerinj at marvell.com>;
> Nithin Kumar Dabilpuram <ndabilpuram at marvell.com>
> Subject: [EXT] Re: [PATCH v5 2/2] app/testpmd: add command to process
> Rx metadata negotiation
> 
> External Email
> 
> ----------------------------------------------------------------------
> On 12/21/2022 2:07 AM, Hanumanth Pothula wrote:
> > Presently, Rx metadata is sent to PMD by default, leading to a
> > performance drop as processing for the same in Rx path takes extra
> > cycles.
> >
> > Hence, add new testpmd command,
> >   'enable port <port_id> nic_to_pmd_rx_metadata'
> >
> > This command helps in sending Rx metadata to PMD and thereby Rx
> > metadata flow command requests are processed.
> >
> > Signed-off-by: Hanumanth Pothula <hpothula at marvell.com>
> 
> Hi Hanumanth,
> 
> I agree with Thomas for the patch.
> 
> 'eth_rx_metadata_negotiate_mp()' requests all Rx metadata offloads to be
> enabled, but at this stage if there is no flow rule for Rx metadata why it is
> consuming extra cycles?
> 
> Can you update driver code to process Rx metadata when it is enabled by
> application (via 'rte_eth_rx_metadata_negotiate()') AND there is at least
> one flow rule for it?

#1 What is the purpose of rte_eth_rx_metadata_negotiate() API if it is always called by testpmd.
We thought it was added so that when that metadata is not needed, application need not call this
thereby saving cycles/bandwidth.

#2 We use this API similar to Rx/Tx offload flags so that we can set things up before device is
configured. We thought that is the purpose of having this negotiate API and avoid depleting offload flags.

#3 Generally any new offloads added to DPDK would be in disabled state in testpmd and we would have
an option to enable it. In this case, testpmd is by default calling this negotiation.

We can update the driver if the purpose of this API is clear.