A set of 71 patches against the Linux kernel provide support for Intel Processor Trace (PT), an Intel CPU etension that provides information about software execution flow. Via the perf subsystem this information is then exposed to user-space and there's an abstraction for it using the "itrace" utility.
For those developers interested in more information on Linux Intel Processor Trace support, see the Linux kernel mailing list.
In terms of Intel PT support, it seems to be a Broadwell CPU feature. More details on Intel PT can be found via this Intel.com page.