OS Time Synchronization

Time-Stamping and Time Synchronization

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IntelĀ® PAC
Napatech SmartNIC
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User Guide

Description

OS time synchronization is absolute time synchronization of the SmartNIC time stamp clock to the system OS time via the PCI bus (described in most of OS Time Synchronization), or synchronization of OS time to a Napatech SmartNIC installed in the server (described in Synchronization of OS time to a Napatech SmartNIC).

Features

OS time synchronization can be individually enabled for each SmartNIC installed in a server. When enabled, the driver initializes the time stamp clock to the OS time at load time, and continuously regulates the clock to synchronize against the current OS time. The control loop runs every 500 milliseconds.

Note: Initially the control loop must be calibrated. This takes approximately 2.5 seconds from the first time skew measurement. No clock adjustments are performed before the calibration is finished. Furthermore, if the algorithm makes a time jump, either initially or because an OS time jump has occurred, the calibration must be done again and 2.5 seconds will expire before clock adjustments are performed.

Convergence time in sliding mode

When sliding is configured using the TimeSyncHardReset parameter (see Enabling and Disabling Time Jumps), the convergence time to synchronization is approximately 500 times the skew between the SmartNIC time and the OS time. If the SmartNIC time is 1 second off the OS time, it takes 500 seconds to get the SmartNIC synchronized. If the skew is large, it may make sense to force the SmartNIC clock into synchronization. The application can force the SmartNIC clock to synchronization by using the NT_CONFIG_PARM_ADAPTER_TIMESYNC_RESET parameter in the configuration stream with the NT_TIMESYNC_RESET_HARD_RESET_TIME_TO_REF command.

An example of a sudden jump in OS time occurs when the OS time is synchronized to NTP and the NTP server connection is lost for a long period and then comes back up.

Maximum time to obtain synchronization in jump mode

The maximum time it takes to obtain a stable saddle point within the jitter accuracy when jumping is allowed using TimeSyncHardReset is approximately 120 seconds.

Guideline

OS time synchronization can be used where a lower accuracy is acceptable.
Note: It is not recommended to enable time jumps when merging across SmartNICs, since jumps backwards in time can lead to merge errors. Sliding must be used instead.

Synchronization of OS time to a Napatech SmartNIC

The OS time can be synchronized to an NT SmartNIC installed in the server. The control loop runs every 500 milliseconds. Only one SmartNIC can be configured as the reference (see OS Time Synchronization to SmartNIC Clock Reference).