[$] Beginning the software-interrupt lock pushdown

The big kernel lock (BKL) is a distant memory now but, for years, it wasone of the more intractable problems faced by the kernel developmentcommunity. The end of the BKL does not mean that the kernel is withoutproblematic locks, however. In recent times, some attention has been paidto the software-interrupt (or "bottom half") lock, which can create latencyproblems, especially on realtime systems. Frederic Weisbecker is taking anew tack in his campaign to cut this lock down to size, with an approachbased on how the BKL was eventually removed.