Date: Mon, 25 Jan 2016 17:55:20 -0600 From: Xiaoye Sun <Xiaoye.Sun@rice.edu> To: freebsd-net@freebsd.org Subject: swaping ring slots between NIC ring and Host ring does not always success Message-ID: <CAJnByzj6Dj3vouZ2NbxqvCV-2-7TVtTR4FaWKuCFaaRN2X%2ByAA@mail.gmail.com>
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Hi all, I wrote a netmap application that is very similar to bridge.c in master/example directory of the netmap code. The major difference between my program and bridge.c is that my application also creates custom packets that are directly put into the tx ring of the NIC (like a packet generator with NIC-Host packet forwarding). Each generated packet has an unique sequence number so that the receiver can tell if a packet is lost. Like bridge.c, the packet forwarding between the nic and the host uses 'zerocopy', so that the program only swaps the buf_idx of the slots to virtually forward the packet to the other end. NS_BUF_CHANGED is set for the slots (both rx and tx) whose buf_idx has been changed due to zerocopy. I set the number of rings on nic to 1 using the ethtool command, i.e., one pair of netmap rings for the nic (one for host tx and one for host rx) and another pair of rings for the host (one for host tx and one for host rx). However, at the receiver side, I found that there is a chance (very little chance, less than 1% of the swaps) where swapping the buf_idx does not success. The receiver might get the packet in the buffer swapped out. For example, the netmap program wants to swap host slot *SH* with NIC slot *SN* in order to send the packet in *SH* from host to the receiver; the receiver might get the packet in *SN* instead. This usually happens to the very end of the available slots. Our experiment is done on *Linux* machine (Linux 3.16.0-4-amd64 #1 SMP Debian 3.16.7-ckt11-1 (2015-05-24) x86_64 GNU/Linux) with* intel NIC* (Intel Corporation 82599ES 10-Gigabit SFI/SFP+ Network Connection) using the *ixgbe* driver. To understand this problem, I look into the patch code to the ixgbe driver. I found that the flag NS_BUF_CHANGED is not used in the linux driver for ixgbe. please look the header file /LINUX/ixgbe_netmap_linux.h. In funtions ixgbe_netmap_txsync and ixgbe_netmap_rxsync, the function call netmap_reload_map is commented out. However, the ixgbe's driver patch for FreeBSD calls the reload function. So, I am wondering if this is a known problem when using netmap on LINUX. Has anybody found the same problem? Is netmap_reload_map required in Linux? why it is not called in the driver patch? What is the recommended solution for this problem? Thanks! Best, Xiaoye
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