netdev - ndo_xdp_xmit - on which queue to transmit the packet (if core_id >= total_xdp

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Message-ID: <DM6PR18MB3388D5F49B3A0A3522A40184ABBA0@DM6PR18MB3388.namprd18.prod.outlook.com>
Date:   Fri, 6 Sep 2019 20:49:20 +0000
From:   Manish Chopra <manishc@...vell.com>
To:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: ndo_xdp_xmit - on which queue to transmit the packet (if core_id >=
 total_xdp_queues ) ?

Hello,

I am working on XDP_REDIRECT implementation and got a query. Some of the ethernet drivers decide the xdp queue index on which xdp packet should be redirected based
on smp_processor_id() in their ndo_xdp_xmit() handler, if smp_processor_id() >= total_num_xdp_queues, they decide to drop the packets and return error from the handler.
I am hitting the same condition where using 8 XDP queues, I get CPU id 8 to redirect the XDP packet and I am not sure if it should be dropped or can be transmitted on a
queue (= smp_processor_id() % total_num_xdp_queues) safely ?.

freescale/dpaa2 seems to be handling this case by sending the packet on the queue (= smp_processor_id() % total_num_xdp_queues) but unsure what should be the expected behavior. 

Regards,
Manish Chopra.