linux-stable.git/kernel/sched.c, branch linux-2.6.18.y

Fix longstanding load balancing bug in the scheduler

2006-10-13T20:23:22+00:00

The scheduler will stop load balancing if the most busy processor contains
processes pinned via processor affinity.

The scheduler currently only does one search for busiest cpu.  If it cannot
pull any tasks away from the busiest cpu because they were pinned then the
scheduler goes into a corner and sulks leaving the idle processors idle.

F.e.  If you have processor 0 busy running four tasks pinned via taskset,
there are none on processor 1 and one just started two processes on
processor 2 then the scheduler will not move one of the two processes away
from processor 2.

This patch fixes that issue by forcing the scheduler to come out of its
corner and retrying the load balancing by considering other processors for
load balancing.

This patch was originally developed by John Hawkes and discussed at
http://marc.theaimsgroup.com/?l=linux-kernel&m=113901368523205&w=2.

I have removed extraneous material and gone back to equipping struct rq
with the cpu the queue is associated with since this makes the patch much
easier and it is likely that others in the future will have the same
difficulty of figuring out which processor owns which runqueue.

The overhead added through these patches is a single word on the stack if
the kernel is configured to support 32 cpus or less (32 bit).  For 32 bit
environments the maximum number of cpus that can be configued is 255 which
would result in the use of 32 bytes additional on the stack.  On IA64 up to
1k cpus can be configured which will result in the use of 128 additional
bytes on the stack.  The maximum additional cache footprint is one
cacheline.  Typically memory use will be much less than a cacheline and the
additional cpumask will be placed on the stack in a cacheline that already
contains other local variable.


Signed-off-by: Christoph Lameter 
Cc: John Hawkes 
Cc: Suresh Siddha 
Cc: Ingo Molnar 
Cc: Nick Piggin 
Cc: Peter Williams 
Signed-off-by: Andrew Morton 
Signed-off-by: Greg Kroah-Hartman

[PATCH] revert "Drop tasklist lock in do_sched_setscheduler"

2006-08-27T18:01:29+00:00

sched_setscheduler() looks at ->signal->rlim[].  It is unsafe do
dereference ->signal unless tasklist_lock or ->siglock is held (or p ==
current).  We pin the task structure, but this can't prevent from
release_task()->__exit_signal() which sets ->signal = NULL.

Restore tasklist_lock across the setscheduler call.

Signed-off-by: Oleg Nesterov 
Cc: Greg KH 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

[PATCH] pi-futex: missing pi_waiters plist initialization

2006-07-31T20:28:41+00:00

Initialize init task's pi_waiters plist.  Otherwise cpu hotplug of cpu 0
might crash, since rt_mutex_getprio() accesses an uninitialized list head.

call chain which led to crash:

take_cpu_down
sched_idle_next
__setscheduler
rt_mutex_getprio

Using PLIST_HEAD_INIT in the INIT_TASK macro doesn't work unfortunately,
since the pi_waiters member is only conditionally present.

Cc: Arjan van de Ven 
Cc: Thomas Gleixner 
Acked-by: Ingo Molnar 
Signed-off-by: Heiko Carstens 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

[PATCH] fix cond_resched() fix

2006-07-31T20:28:40+00:00

In cond_resched_lock() it calls __resched_legal() before dropping the spin
lock.  __resched_legal() will always finds the preempt_count non-zero and
will prevent the call to __cond_resched().

The attached patch adds a parameter to __resched_legal() with the expected
preempt_count value.

Cc: Ingo Molnar 
Cc: 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

[PATCH] sched: build_sched_domains() fix

2006-07-31T20:28:36+00:00

Use the correct groups while initializing sched groups power for
allnodes_domain.  This fixes the crash observed while creating exclusive
cpusets.

Signed-off-by: Suresh Siddha 
Reported-and-tested-by: Paul Jackson 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

[PATCH] per-task-delay-accounting: cpu delay collection via schedstats

2006-07-15T04:53:56+00:00

Make the task-related schedstats functions callable by delay accounting even
if schedstats collection isn't turned on.  This removes the dependency of
delay accounting on schedstats.

Signed-off-by: Chandra Seetharaman 
Signed-off-by: Shailabh Nagar 
Signed-off-by: Balbir Singh 
Cc: Jes Sorensen 
Cc: Peter Chubb 
Cc: Erich Focht 
Cc: Levent Serinol 
Cc: Jay Lan 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

[PATCH] per-task-delay-accounting: sync block I/O and swapin delay collection

2006-07-15T04:53:56+00:00

Unlike earlier iterations of the delay accounting patches, now delays are only
collected for the actual I/O waits rather than try and cover the delays seen
in I/O submission paths.

Account separately for block I/O delays incurred as a result of swapin page
faults whose frequency can be affected by the task/process' rss limit.  Hence
swapin delays can act as feedback for rss limit changes independent of I/O
priority changes.

Signed-off-by: Shailabh Nagar 
Signed-off-by: Balbir Singh 
Cc: Jes Sorensen 
Cc: Peter Chubb 
Cc: Erich Focht 
Cc: Levent Serinol 
Cc: Jay Lan 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

[PATCH] lockdep: core, fix rq-lock handling on __ARCH_WANT_UNLOCKED_CTXSW

2006-07-15T04:53:55+00:00

On platforms that have __ARCH_WANT_UNLOCKED_CTXSW set and want to implement
lock validator support there's a bug in rq->lock handling: in this case we
dont 'carry over' the runqueue lock into another task - but still we did a
spinlock_release() of it.  Fix this by making the spinlock_release() in
context_switch() dependent on !__ARCH_WANT_UNLOCKED_CTXSW.

(Reported by Ralf Baechle on MIPS, which has __ARCH_WANT_UNLOCKED_CTXSW.
This fixes a lockdep-internal BUG message on such platforms.)

Signed-off-by: Ingo Molnar 
Cc: Ralf Baechle 
Cc: Arjan van de Ven 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

[PATCH] small kernel/sched.c cleanup

2006-07-10T20:24:13+00:00

- constify and optimize stat_nam (thanks to Michael Tokarev!)
- spelling and comment fixes

Signed-off-by: Andreas Mohr 
Acked-by: Ingo Molnar 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

[PATCH] sched: fix bug in __migrate_task()

2006-07-10T20:24:13+00:00

Problem:

In the function __migrate_task(), deactivate_task() followed by
activate_task() is used to move the task from one run queue to
another.  This has two undesirable effects:

1. The task's priority is recalculated. (Nowhere else in the
scheduler code is the priority recalculated for a change of CPU.)

2. The task's time stamp is set to the current time.  At the very least,
this makes the adjustment of the time stamp before the call to
deactivate_task() redundant but I believe the problem is more serious
as the time stamp now holds the time of the queue change instead of
the time at which the task was woken.  In addition, unless dest_rq is
the same queue as "current" is on the time stamp could be inaccurate
due to inter CPU drift.

Solution:

Replace the call to activate_task() with one to __activate_task().

Signed-off-by: Peter Williams 
Cc: Ingo Molnar 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds