illumos gate

There is a large body of software today which calls clock_gettime() with extremely high frequency. On many operating systems, this functionality is implemented in such a way that it's performed entirely in userspace (via the vDSO on Linux), cutting down on the cost. This is not the case for illumos, which relies on the normal syscall path. On modern x86 hardware, clock_gettime() takes 30-50ns on Linux whereas on illumos, it's closer to 250ns+.

In order for software which heavily relies on frequent clock access, it would be nice to have access to the time via a userspace-only mechanism.
This has been implemented in SmartOS as OS-5192.
Various fixes and updates have been made to it in subsequent tickets.