Re: [PATCH] update: preemptive kernel for O(1) sched

[Robert Love <rml@tech9.net>]

A version of preempt-stats for the 2.5 series kernel is available at:

	ftp://ftp.kernel.org/pub/linux/kernel/people/rml/preempt-stats

and your favorite mirror.  Patches for 2.4 are available, too.

This patch, used on top of preempt-kernel, allows the measuring of
periods of non-preemptible so that we can identify long-held locks.  The
patch creates a proc entry, latencytimes, which contains the top 20
worst-case recorded periods since it was last read.  To begin recording,
read the file once.  Subsequent reads will return the results. I.e.,

[23:25:08]rml@langston:~$ cat /proc/latencytimes 
Worst 20 latency times of 277 measured in this period.
  usec      cause     mask   start line/file      address   end line/file
  9982  spin_lock        0   488/sched.c         c0117ee2   645/irq.c
   968        BKL        0   666/tty_io.c        c0193d58   645/irq.c
   430  spin_lock        0    69/i387.c          c010f34f    96/mmx.c
   103       ide0        0   583/irq.c           c010ab1c   645/irq.c
   100        BKL        0  2562/buffer.c        c014abda  2565/buffer.c
    54        BKL        0   702/tty_io.c        c019406b   704/tty_io.c
... etc

The goal would be to identity the problem areas and fix them.

	Robert Love