PSPacer/HT version 1.0

Precise Software Pacer (PSPacer)/High-resolution Timer version 1.0 is released on Oct. 22, 2010.

What is PSPacer/HT?

PSPacer/HT is a new derived version of PSPacer which is a qdisc module which realizes precise transmission bandwidth control.

PSPacer is a very useful tool to fully utilize the network bandwidth. However, PSPacer has the following limitations in general use. (1) PSPacer essentially requires the system to fully fill the network pipe with packets. Therefore, the system has to have the capability to transmit packets at the wire rate. For instance, if a Gigabit Ethernet NIC is connected through a 33MHz/32bit PCI bus, the bottleneck is thus PCI bus, and then the system can not transmit packets at 1 gigabit per second. As a result, the output traffic becomes imprecise. (2) PSPacer uses the IEEE 802.3x PAUSE frame as a gap packet. Therefore, PSPacer only works on Ethernet. And also, PAUSE frames can not be used for the original purpose. Therefore, the IEEE 802.3x flow control can not stop transmission from the switch and/or router to the PC. (3) PSPacer can not support pseudo network devices such as bonding and tap devices, because these devices can not properly handle gap packets.

In order to resolve the above limitations of the original PSPacer, PSPacer/HT (High-resolution Timer) controls inter packet gaps by using a high-resolution timer (hrtimer) instead of gap packets. PSPacer/HT determines the transmission timing of a packet and then registers the timing as a high-resolution timer event. When the event is activated, the packet is transmitted.

NOTE: We recommend to use Linux kernel 2.6.31 and later. In Linux kernel 2.6.21 and earlier, the packet scheduling subsystem used the low-resolution timer with a jiffies resolution. In Linux kernel 2.6.22 and later, it was changed to use hrtimer. After kernel 2.6.31, the timer resolution improved from 1 microsecond to 1/16 microsecond.

Tested Environment

We have tested this package in the following environments:

• CentOS 5 (kernel 2.6.31.13 + iproute2 ss061002)
• Ubuntu 9.04 (kernel 2.6.27 + iproute2 ss080417)
• Debian GNU/Linux (kernel 2.6.34 + iproute2 ss100519)

Software Distribution

PSPacer/HT is released under the GNU GPL license, and you can get it from the download page.

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