Re: [Linuxptp-users] [issue] phc2sys results large jitter with multiple '-c'

[egg c. <egg...@gm...>]

Dear Miro,

> Yes, it's related to PCIe delays. The problem is that the kernel
> doesn't provide an ioctl to measure offset between two PHCs, so
> phc2sys has to do it in user space using clock_gettime(), which
> doesn't work very well (large delay, jitter and asymmetry).

Yes it seems like the clock_gettime() api is not very accurate,
the delay introduced by the switchover between userspace
and kernel space may vary a lot. But it's confusing me that
when I run several independent phc2sys instances at the
same time, every one just looks fine, the offset value varies
in the range of two-digit nanoseconds.

Let me do more tests to locate the problem.

Regards,
Yuezhen Luan