On 07/06/2011 03:40 AM, Lynch, Jonathan wrote: > Hi Alex, > > Quick question on when RXMPC is incremented on 82599 hardware. > Does the hardware check if RDH[n] == RDT[n]. If this is true there are > no descriptors free, hence packet dropped, RXMPC[n]++? > > 8.2.3.23.4 Rx Missed Packets Count — RXMPC[n] (0x03FA0 + 4*n, n=0...7; > RC) DBU-Rx > Register ‘n’ counts the number of missed packets per packet buffer ‘n’. > Packets are missed when the receive FIFO has insufficient space to > store the incoming > packet. This may be caused due to insufficient buffers allocated, or > because there is > insufficient bandwidth on the IO bus. Events setting this counter also > set the receiver > overrun interrupt (RXO). These registers do not increment if receive > is not enabled and > count only packets that would have been posted to the SW driver. > > Regards > Jonathan
RXMPC is incremented any time the RX FIFO is filled and a packet is received that cannot be placed on the FIFO. It does not check RDH/RDT values. There are two ways to end up with the RX FIFO being filled. The first way to fill the RX FIFO is if the software cannot keep up. This results in the RDH[n] == RDT[n] scenerio that you described above, but what this triggers is packets to start waiting in the RX FIFO for free space. In order for this to occur you also need to have the SRRCTL.DROP_EN bit cleared in order to prevent the packet from being dropped at the head of the FIFO for not having a free descriptor. The second way to fill the RX FIFO is if the PCIe bus is somehow limited and cannot move the packets from the RX FIFO into the system memory fast enough. This can happen if for example you are on a x4 or smaller PCIe link, or possibly on a PCIe gen 1 link. Thanks, Alex ------------------------------------------------------------------------------ All of the data generated in your IT infrastructure is seriously valuable. Why? It contains a definitive record of application performance, security threats, fraudulent activity, and more. Splunk takes this data and makes sense of it. IT sense. And common sense. http://p.sf.net/sfu/splunk-d2d-c2 _______________________________________________ E1000-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/e1000-devel To learn more about Intel® Ethernet, visit http://communities.intel.com/community/wired
