Hi all, I sent this mail yesterday, but it did not be delivered. So I resend it. I am sorry if you receive duplicate mails.
What is PSPacer? PSPacer (Precise Software Pacer) is a qdisc module which realizes precise transmission bandwidth control. It makes bursty traffic which is often generated by TCP smooth without any special hardware. Bursty traffic can degrade the communication performance, because it causes buffer overflow at intermediate network nodes and results in packet losses. In a bursty traffic, packets are sent back to back. By adding a short pause in between the packets, traffic bursts can be avoided. PSPacer controls the interval between outgoing packets very precisely. The key idea of PSPacer is to determine transmission timing of packets by the number of bytes transferred. If packets are transferred back to back, the timing a packet is sent can be determined by the number of bytes sent before the packet. PSPacer fills the gaps between time aligned "real packets" (the packets which are sent by user program) by "gap packets". The real packets and gap packets are sent back to back, and thus the timing of transmission of each real packet can be precisely controlled by adjusting the gap packet size. As the gap packets, the IEEE 802.3x PAUSE frames are used. PAUSE frames are discarded at a switch input port, and only real packets go through the switch keeping the original intervals. In the past, some software-based pacing schemes have been proposed. These schemes use timer interrupt based packet transmission timing control. Therefore, to achieve precise pacing, they require the operating system to maintain a high resolution timer, which could incur a large overhead. The patchset consists of two parts: one part is to be applied to the Linux kernel, and the other is to be applied to the iproute2. For detailed description and the usage of PSPacer, please refer to our project page (http://www.gridmpi.org/gridtcp.jsp), and the paper "Design and Evaluation of Precise Software Pacing Mechanisms for Fast Long-Distance Networks," in PFLDnet2005. Usage - setup qdiscs (add the PSPacer qdisc as the root qdisc) # /sbin/tc qdisc add dev eth0 root handle 1: psp default 1 (add the PSPacer class whose target rate is 500Mbps) # /sbin/tc class add dev eth0 parent 1: classid 1:1 psp rate 500mbit (add the PFIFO qdisc as the sub qdisc) # /sbin/tc qdisc add dev eth0 parent 1:1 handle 10: pfifo - run iperf (to confirm the effect of PSPacer) $ iperf -c 192.168.1.2 -i 10 -t 60 ------------------------------------------------------------ Client connecting to 192.168.1.2, TCP port 5122 TCP window size: 16.0 KByte (default) iperf shows payload bandwidth. 476Mbps is the payload bandwidth when the physical layer bandwidth is 500Mbps and packet size is 1500Bytes ------------------------------------------------------------ [ 3] local 192.168.1.1 port 46457 connected with 192.168.1.2 port 5122 [ 3] 0.0-10.0 sec 567 MBytes 476 Mbits/sec [ 3] 10.0-20.0 sec 567 MBytes 476 Mbits/sec - cleanup qdiscs (remove the PFIFO sub qdisc) # /sbin/tc qdisc del dev eth0 parent 1:1 handle 10: (remove the PSPacer class) # /sbin/tc class del dev eth0 parent 1: classid 1:1 (remove the PSPacer qdisc) # /sbin/tc qdisc del dev eth0 root handle 1: (remove the PSPacer module) # /sbin/rmmod sch_psp Limitations (1) PSPacer controls the bandwidth according to the ratio of the target bandwidth in the maximum transmission bandwidth of the system. Therefore, the system (computer, network interface, operating system, buffer settings, etc.) should have a capability to transmit packets at the maximum transmission rate (i.e. 1 Gbps for 1000BASE, 100 Mbps for 100BASE) to realize a precise pacing. Therefore, if you want to control Gigabit Ethernet traffic, we recommend to use PCI-X, 66MHz/64bit PCI or CSA connected network interface. If the total of target bandwidth of the output streams is less than 100Mbps, you can set the network interface to use 100BASE mode so as to obtain precise pacing. For the same reason, avoid using a shared switch (dumb hub) for the edge switch to which the PC with PSPacer is connected. (2) PSPacer uses the IEEE 802.3x PAUSE frame as the gap between packets. Therefore, you can not use the PAUSE frame to stop transmission from the switch/router to the PC. Since PSPacer generates PAUSE frames with zero pause time, there should not be any side effects other than you can not stop transmission from the switch. However, it is recommended to disable IEEE 802.3x flow control function of the switch (to which a PC with PSPacer is connected) in order to avoid unexpected behavior. (3) PSPacer does not support TCP Segmentation Offloading (TSO). You have to disable TSO by using the ethtool command (ethtool -K eth0 tso off). Best regards, Ryousei Takano - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
