Per-task delay accounting

The following patches add accounting for the delays seen by tasks in
a) waiting for a CPU (while being runnable)
b) completion of synchronous block I/O initiated by the task
c) swapping in pages (i.e. capacity misses).

Such delays provide feedback for a task's cpu priority, io priority and
rss limit values. Long delays, especially relative to other tasks, can
be a trigger for changing a task's cpu/io priorities and modifying its
rss usage (either directly through sys_getprlimit() that was proposed
earlier on lkml or by throttling cpu consumption or process calling
sys_setrlimit etc.)

The major changes since the previous posting of these patches are

- use of the new generic netlink interface (NETLINK_GENERIC family)
with provision for reuse by other (non-delay accounting) kernel
components
- sysctl option for turning delay accounting collection on/off
dynamically
- similar sysctl option for schedstats. Delay accounting leverages
schedstats code for cpu delays.
- dynamic allocation of delay accounting structures

More comments in individual patches. Please give feedback.

--Shailabh

Series
nstimestamp-diff.patch
schedstats-sysctl.patch
delayacct-setup.patch
delayacct-sysctl.patch
delayacct-blkio.patch
delayacct-swapin.patch
delayacct-genetlink.patch