[$] (Nearly) full tickless operation in 3.10
On a typical Linux system, each running CPU will be diverted between 100
and 1000 times each second by the periodic timer interrupt. That interrupt
is the CPU's cue to reconsider which process should be running, catch up
with read-copy-update (RCU) callbacks, and generally handle any necessary
housekeeping. This periodic "tick" can be reasonably compared to the
infamous big kernel lock (BKL): it is convenient to have around, but it
also has an effect on performance that makes developers wish to abolish it.
The key difference might be that getting rid of the timer tick has taken
rather longer than was required to eliminate the BKL. The 3.10 kernel will
take an important step in that direction, though, with the addition of the
"full NOHZ" mode — but a lot of limitations still apply.