Re: [PATCH net-next v6 02/10] dpaa_eth: add support for DPAA Ethernet

From: Madalin-Cristian Bucur <madalin.bucur@nxp.com>
Date: Mon, 7 Nov 2016 16:32:16 +0000

quoted

-----Original Message-----
From: David Miller [mailto:davem@davemloft.net]
Sent: Monday, November 07, 2016 5:55 PM

From: Madalin-Cristian Bucur <madalin.bucur@nxp.com>
Date: Mon, 7 Nov 2016 15:43:26 +0000

quoted

quoted

From: David Miller [mailto:davem@davemloft.net]
Sent: Thursday, November 03, 2016 9:58 PM

Why?  By clearing this, you disallow an important fundamental way to do
performane testing, via pktgen.

The Tx path in DPAA requires one to insert a back-pointer to the skb

into

quoted

the Tx buffer. On the Tx confirmation path the back-pointer in the

buffer

quoted

is used to release the skb. If Tx buffer is shared we'd alter the back-

pointer

quoted

and leak/double free skbs. See also

Then have your software state store an array of SKB pointers, one for each
TX ring entry, just like every other driver does.

There is no Tx ring in DPAA. Frames are send out on QMan HW queues towards
the FMan for Tx and then received back on Tx confirmation queues for cleanup.
Array traversal would for sure cost more than using the back-pointer. Also,
we can now process confirmations on a different core than the one doing Tx,
we'd have to keep the arrays percpu and force the Tx conf on the same core.
Or add locks.

Report back an integer index, like every scsi driver out there which
completes tagged queued block I/O operations asynchronously.  You can
associate the array with a specific TX confirmation queue.