Permutation-write: Optimizing write performance and energy for skyrmion racetrack memory

Skyrmion racetrack memory (Sky-RM) is an emerging non-volatile memory technology that offers not only high-density data storage but also the feature of shifting data along a racetrack by current. However, compared to other shifting based manipulations, writing/injecting new particle-like Skyrmions is much more time-consuming and energy-hungry. To optimize the write performance and energy for Sky-RM, this paper introduces a new write strategy, called Permutation-Write. Specifically, this strategy circumvents new Skyrmion injections during data writes by "re-permuting"existing Skyrmion particles in the racetrack. Evaluation results show that Permutation-Write strategy can significantly reduce the number of expensive Skyrmion injections by at least 50% compared to other state-of-the-art write reduction strategies, and merely introduce 2.25 injections on average for every 64-bit-word write under realistic workloads.