[PATCH] smptimers, old BH removal, tq-cleanup

This is the smptimers patch plus the removal of old BHs and a rewrite of
task-queue handling.

Basically with the removal of TIMER_BH i think the time is right to get
rid of old BHs forever, and to do a massive cleanup of all related
fields.  The following five basic 'execution context' abstractions are
supported by the kernel:

  - hardirq
  - softirq
  - tasklet
  - keventd-driven task-queues
  - process contexts

I've done the following cleanups/simplifications to task-queues:

 - removed the ability to define your own task-queue, what can be done is
   to schedule_task() a given task to keventd, and to flush all pending
   tasks.

This is actually a quite easy transition, since 90% of all task-queue
users in the kernel used BH_IMMEDIATE - which is very similar in
functionality to keventd.

I believe task-queues should not be removed from the kernel altogether.
It's true that they were written as a candidate replacement for BHs
originally, but they do make sense in a different way: it's perhaps the
easiest interface to do deferred processing from IRQ context, in
performance-uncritical code areas.  They are easier to use than
tasklets.

code that cares about performance should convert to tasklets - as the
timer code and the serial subsystem has done already. For extreme
performance softirqs should be used - the net subsystem does this.

and we can do this for 2.6 - there are only a couple of areas left after
fixing all the BH_IMMEDIATE places.

i have moved all the taskqueue handling code into kernel/context.c, and
only kept the basic 'queue a task' definitions in include/linux/tqueue.h.
I've converted three of the most commonly used BH_IMMEDIATE users:
tty_io.c, floppy.c and random.c. [random.c might need more thought
though.]

i've also cleaned up kernel/timer.c over that of the stock smptimers
patch: privatized the timer-vec definitions (nothing needs it,
init_timer() used it mistakenly) and cleaned up the code. Plus i've moved
some code around that does not belong into timer.c, and within timer.c
i've organized data and functions along functionality and further
separated the base timer code from the NTP bits.

net_bh_lock: i have removed it, since it would synchronize to nothing. The
old protocol handlers should still run on UP, and on SMP the kernel prints
a warning upon use. Alexey, is this approach fine with you?

scalable timers: i've further improved the patch ported to 2.5 by wli and
Dipankar. There is only one pending issue i can see, the question of
whether to migrate timers in mod_timer() or not. I'm quite convinced that
they should be migrated, but i might be wrong. It's a 10 lines change to
switch between migrating and non-migrating timers, we can do performance
tests later on. The current, more complex migration code is pretty fast
and has been stable under extremely high networking loads in the past 2
years, so we can immediately switch to the simpler variant if someone
proves it improves performance. (I'd say if non-migrating timers improve
Apache performance on one of the bigger NUMA boxes then the point is
proven, no further though will be needed.)

1 files changed, 0 insertions, 2 deletions

diff --git a/lib/bust_spinlocks.c b/lib/bust_spinlocks.c
index 07f3eda219f8..6bb7319e09a0 100644
--- a/lib/bust_spinlocks.c
+++ b/lib/bust_spinlocks.c
@@ -14,11 +14,9 @@
 #include <linux/wait.h>
 #include <linux/vt_kern.h>
 
-extern spinlock_t timerlist_lock;
 
 void bust_spinlocks(int yes)
 {
-	spin_lock_init(&timerlist_lock);
 	if (yes) {
 		oops_in_progress = 1;
 	} else {