> From: David Miller [mailto:da...@davemloft.net] > Sent: Monday, November 07, 2016 6:40 PM > > From: Madalin-Cristian Bucur <madalin.bu...@nxp.com> > Date: Mon, 7 Nov 2016 16:32:16 +0000 > > >> From: David Miller [mailto:da...@davemloft.net] > >> Sent: Monday, November 07, 2016 5:55 PM > >> > >> From: Madalin-Cristian Bucur <madalin.bu...@nxp.com> > >> Date: Mon, 7 Nov 2016 15:43:26 +0000 > >> > >> >> From: David Miller [mailto:da...@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 > >> > the Tx buffer. On the Tx confirmation path the back-pointer in the > >> > buffer > >> > is used to release the skb. If Tx buffer is shared we'd alter the > >> > back-pointer > >> > 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.
>From HW? It only gives you back the buffer start address (plus length, etc). "buff_2_skb()" needs to be solved in SW, expensively using array (lists? As the number of frames in flight can be large/variable) or cheaply with the back pointer. The back-pointer approach has its tradeoffs: no shared skbs, imposed non-zero needed_headroom.
