[pclmulqdq]

I was personally pretty surprised at the idea that Jane Street found PTP to be too difficult to administer or run. Hardware support for PTP is nearly ubiquitous in NICs and switches (unless you build this gear for yourself, I guess), so it is not that hard to administer. PTP done poorly gets you ~100 ns time sync across your cluster, and if you do everything correctly you can get time within about 10 ns given how small a trading network is.

[AdamN]

This time accuracy would need to propagate to all their hosts, not just the ones in a single DC. I presume they have hosts in the EU, London, NYC/NJ, Tokyo, Chicago, etc... I imagine 100ns accuracy with that kind of global installation diversity isn't straightforward.

[pclmulqdq]

The gold standard for PTP is to use separate GPS-disciplined atomic clocks in your separate points of presence, and PTP within each one. These are about $10k each, so it is not that expensive even if you have 100 datacenters.

[namibj]

Yes it is, GPS is 1foot ~ 1ns; thus a few ns are trivial with a vaguely decent receiver.