I am trying to use the timestamping function of the Intel I350-T2 1 Gbps adapter and igb driver to put a hardware timestamp in the sk_buff of ALL received frames. Note that I am NOT doing this for PTP, but rather to obtain more accurate frame arrival timestamps to use in code I am developing for higher layers in the TCP/IP protocol stack.
All this seems to be working fine, but I am at a loss to explain the curious distributions of timestamp values I have recorded from the arriving sk_buffs. At high frame rates (>= 800 Mbps) the delta between successive timestamps is quite stable and reflects the expected inter-frame gaps. However, at low frame rates (<= 250 Mbps) the delta between successive timestamps essentially behaves like a random process with a high variance (I should mention that I am controlling the frame sending rate so I know what inter-frame gaps I expect to measure at the receiver). So far, I only have measurements at these two extremes so I don't know anything about how accuracy varies over the entire range of arrival rates. I had expected the timestamps to have the same accuracy independent of the frame arrival rate. Do you have any ideas about why I might be seeing this behavior? The details of my configuration are given below. Any help you can give will be greatly appreciated. -- Don Smith -- F. Donelson Smith (Don) (919) 962-1884 Research Professor [email protected] Department of Computer Science www.cs.unc.edu/~smithfd University of North Carolina at Chapel Hill ========================================================================== Kernel (RHEL 6.4) on Dell R710 system uname -r 2.6.32-358.11.1.el6.x86_64 Adapter (Intel I350-T2): ethtool -i p6p1 driver: igb version: 4.0.1-k firmware-version: 1.63, 0x0a608000 ethtool -k p6p1 Features for p6p1: rx-checksumming: on tx-checksumming: on scatter-gather: on tcp-segmentation-offload: off udp-fragmentation-offload: off generic-segmentation-offload: off generic-receive-offload: off large-receive-offload: off rx-vlan-offload: on tx-vlan-offload: on ntuple-filters: off receive-hashing: on ethtool -c p6p1 Coalesce parameters for p6p1: Adaptive RX: off TX: off stats-block-usecs: 0 sample-interval: 0 pkt-rate-low: 0 pkt-rate-high: 0 rx-usecs: 3 rx-frames: 0 rx-usecs-irq: 0 rx-frames-irq: 0 (Note: all the rest have value 0) ------------------------------------------------------------------------------ This SF.net email is sponsored by Windows: Build for Windows Store. http://p.sf.net/sfu/windows-dev2dev _______________________________________________ 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
