netdev - RE: [net-next PATCH v1 1/3] net: sched: af_packet support for direct ring access

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Date:	Tue, 7 Oct 2014 16:46:11 +0000
From:	"Zhou, Danny" <danny.zhou@...el.com>
To:	Alexei Starovoitov <alexei.starovoitov@...il.com>
CC:	Willem de Bruijn <willemb@...gle.com>,
	John Fastabend <john.fastabend@...il.com>,
	Daniel Borkmann <dborkman@...hat.com>,
	"Florian Westphal" <fw@...len.de>,
	"gerlitz.or@...il.com" <gerlitz.or@...il.com>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	Network Development <netdev@...r.kernel.org>,
	"Ronciak, John" <john.ronciak@...el.com>,
	"Amir Vadai" <amirv@...lanox.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: RE: [net-next PATCH v1 1/3] net: sched: af_packet support for
 direct ring access


> -----Original Message-----
> From: Alexei Starovoitov [mailto:alexei.starovoitov@...il.com]
> Sent: Wednesday, October 08, 2014 12:33 AM
> To: Zhou, Danny
> Cc: Willem de Bruijn; John Fastabend; Daniel Borkmann; Florian Westphal; gerlitz.or@...il.com; Hannes Frederic Sowa; Network
> Development; Ronciak, John; Amir Vadai; Eric Dumazet; David S. Miller
> Subject: Re: [net-next PATCH v1 1/3] net: sched: af_packet support for direct ring access
> 
> On Tue, Oct 7, 2014 at 8:21 AM, Zhou, Danny <danny.zhou@...el.com> wrote:
> >
> > As a master driver, the NIC kernel driver still takes control of flow director as a ethtool backend. Generally,
> > not all queues are initialized and used by NIC kernel driver, which reports actually used rx/tx numbers to stacks.
> > Before splitting off certain queues, if you want use ethtool to direct traffics to those unused queues,
> > ethtool reports invalid argument. Once certain stack-unaware queues are allocated for user space slave driver,
> > ethtool allows directing packets to them as the NIC driver maintains a data struct about which queues are visible
> > and used by kernel, which are used by user space.
> 
> this whole thing sounds like it's a way to let DPDK apps share physical
> interfaces with kernel, so that tcp-based control plane traffic
> can reach DPDK process via kernel while DPDK user space
> data path does the rest of packet processing?
> One still needs pcie register i/o and all of user space driver support
> to make it work, right?
> I guess that's great for DPDK users, but I don't think it's good for linux.

No, it is a generic NIC resource(e.g. rx/tx queue pairs) portioning mechanism among NIC kernel and user space drivers with 
different performance/latency/jitter characteristics. One only needs write efficient packet rx/tx routines by taking advantage
of whatever software optimizations, to manipulate limited rx/tx queue relevant registers on PCIe I/O space. In other words, no 
need to port the entire NIC driver from kernel to user space.