Ceph has a lot of small ops, where lock and cache contention becomes very significant. (Basically a small piece of data/request comes in from the network and the OSD [object storage daemon] network thread has to pass it to the I/O worker thread and then forget it. The I/O thread similarly just needs to get the request issue a read/write, and let the kernel work.)

Since the whole Ceph I/O model is async the less waiting, scheduling, contention, etc. happens the better.

Currently Ceph is CPU bound, that's why they are trying to improve CPU perf.