Date: Mon, 19 Sep 2011 19:43:44 +0200 From: "K. Macy" <kmacy@freebsd.org> To: freebsd-drivers@freebsd.org Subject: Fwd: Multiple TX queue support in nic driver Message-ID: <CAHM0Q_Oyqt11cGek0PKKFYTZ6Gw-h0VLWndoCOW874H%2BVJ3y_Q@mail.gmail.com> In-Reply-To: <CAHM0Q_MHjXu8Z0-0Zw4Lovgx0H=WAtVRGe1nGp9F7sdfcDwLtg@mail.gmail.com> References: <201109190813.37817.jhb@freebsd.org> <CAHM0Q_MHjXu8Z0-0Zw4Lovgx0H=WAtVRGe1nGp9F7sdfcDwLtg@mail.gmail.com>
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forwarding response to the list > ---------- Forwarded message ---------- > From:=A0Naresh <gbal.naresh@gmail.com> > To:=A0"freebsd-drivers@freebsd.org" <freebsd-drivers@freebsd.org> > Date:=A0Thu, 15 Sep 2011 20:26:16 +0530 > Subject:=A0Multiple TX queue support in nic driver > Hi All, > > I am working on a 10G Ethernet driver. =A0I have a requirement to support= multiple TX queues. I looked into IXGBE and CXGB drivers for reference, I = have some questions regarding the implementation. > > 1) For supporting multiple TXQs, I see the above mentioned drivers create= a ring buffer in the driver for each hardware TX queue, and queue the pack= ets from stack to the ring buffer before queueing on the hardware queue. I = don't understand why to create a ring buffer for supporting multiple TXQS. = There might be a very good reason for them to do that way, but I am unable = to get that. The software queues are only used if the txq lock is already held by another thread. What alternative are you thinking of? Waiting for the txq lock would be much slower than a simple ring buffer enqueue. A global queue where threads randomly pulled off and put on an available txq would cause packet reording within individual flows. > Is it ok to queue the packets to hardware queue directly based on the flo= wid supplied in the mbuf =A0packet header in if_transmit routine ? Yes. This is what those drivers already do if the txq lock is not held. > 2) Regarding flowid, for the first TX packet the flowid is not set and th= e packet goes out on the default TX queue and when the corresponding RX res= ponse comes to hardware it queues =A0 the packet to appropriate RXQ based o= n the rss hash. The driver then before posting RX packet to stack it should= set the flowid in packet to RXQ index. > After that the TX packets from stack for that TCP connection will come wi= th flowid supplied by us. Is this understanding correct ? Yes. For using multiple queues with UDP unidirectionally one needs to either use the flowtable or change the inpcb creation routine. Cheers
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