Re: [Linuxptp-users] Syncing multiple NICs on the same server

[Wojtek W. <ww...@nv...>]

> There is a caveat here : I assume both the ports on the same NIC (mlnx1 and mlnx2 for example)
> have the same hardware clock source even though under /dev/ they are mapped to different ptp
> files i.e /dev/ptp8 and /dev/ptp9 respectively.

Depending on the configuration of the Mellanox NIC, the PHC exposed for different ports will either be the same PHC (in Real-Time Clock mode) - though exposed through two /dev/ files or (in non-Real-Time Clock mode) driver will construct separate PHCs for each of the ports. 
You can find some instructions on how to configure it here: https://docs.nvidia.com/networking/display/NVIDIA5TTechnologyUserManualv10/Real-Time+Clock
And some general documentation on the Real-Time Clock here: https://docs.nvidia.com/networking/display/NVIDIA5TTechnologyUserManualv10/Real+Time+Clock

> There are some jitters / unexpected outliers which I attribute to measurement uncertainties / syscall jitter. 
99% of what you're seeing is likely PCIe read latency jitter. This is the reason why phc2sys has the '-N' option to mitigate the problem:
> -N phc-num
>   Specify the number of master clock readings per one slave clock update.
>   Only the fastest reading is used to update the slave clock, this is useful
>   to minimize the error caused by random delays in scheduling and bus utilization.

W