linux-toradex.git/kernel/sched_fair.c, branch v2.6.38-rc2

sched: Fix signed unsigned comparison in check_preempt_tick()

2011-01-18T14:09:44+00:00

Signed unsigned comparison may lead to superfluous resched if leftmost
is right of the current task, wasting a few cycles, and inadvertently
_lengthening_ the current task's slice.

Reported-by: Venkatesh Pallipadi 
Signed-off-by: Mike Galbraith 
Signed-off-by: Peter Zijlstra 
LKML-Reference: <1294202477.9384.5.camel@marge.simson.net>
Signed-off-by: Ingo Molnar

sched: Update effective_load() to use global share weights

2011-01-18T14:09:38+00:00

Previously effective_load would approximate the global load weight present on
a group taking advantage of:

entity_weight = tg->shares ( lw / global_lw ), where entity_weight was provided
by tg_shares_up.

This worked (approximately) for an 'empty' (at tg level) cpu since we would
place boost load representative of what a newly woken task would receive.

However, now that load is instantaneously updated this assumption is no longer
true and the load calculation is rather incorrect in this case.

Fix this (and improve the general case) by re-writing effective_load to take
advantage of the new shares distribution code.

Signed-off-by: Paul Turner 
Signed-off-by: Peter Zijlstra 
LKML-Reference: <20110115015817.069769529@google.com>
Signed-off-by: Ingo Molnar

sched: Fix interactivity bug by charging unaccounted run-time on entity re-weight

2010-12-19T15:36:30+00:00

Mike Galbraith reported poor interactivity[*] when the new shares distribution
code was combined with autogroups.

The root cause turns out to be a mis-ordering of accounting accrued execution
time and shares updates.  Since update_curr() is issued hierarchically,
updating the parent entity weights to reflect child enqueue/dequeue results in
the parent's unaccounted execution time then being accrued (vs vruntime) at the
new weight as opposed to the weight present at accumulation.

While this doesn't have much effect on processes with timeslices that cross a
tick, it is particularly problematic for an interactive process (e.g. Xorg)
which incurs many (tiny) timeslices.  In this scenario almost all updates are
at dequeue which can result in significant fairness perturbation (especially if
it is the only thread, resulting in potential {tg->shares, MIN_SHARES}
transitions).

Correct this by ensuring unaccounted time is accumulated prior to manipulating
an entity's weight.

[*] http://xkcd.com/619/ is perversely Nostradamian here.

Signed-off-by: Paul Turner 
Signed-off-by: Peter Zijlstra 
Cc: Mike Galbraith 
Cc: Linus Torvalds 
LKML-Reference: <20101216031038.159704378@google.com>
Signed-off-by: Ingo Molnar

sched: Move periodic share updates to entity_tick()

2010-12-19T15:36:22+00:00

Long running entities that do not block (dequeue) require periodic updates to
maintain accurate share values.  (Note: group entities with several threads are
quite likely to be non-blocking in many circumstances).

By virtue of being long-running however, we will see entity ticks (otherwise
the required update occurs in dequeue/put and we are done).  Thus we can move
the detection (and associated work) for these updates into the periodic path.

This restores the 'atomicity' of update_curr() with respect to accounting.

Signed-off-by: Paul Turner 
Signed-off-by: Peter Zijlstra 
LKML-Reference: <20101216031038.067028969@google.com>
Signed-off-by: Ingo Molnar

Merge branch 'linus' into sched/core

2010-12-08T19:15:29+00:00

Merge reason: we want to queue up dependent cleanup

Signed-off-by: Ingo Molnar

Merge commit 'v2.6.37-rc3' into sched/core

2010-11-26T14:05:21+00:00

Merge reason: Pick up latest fixes.

Signed-off-by: Ingo Molnar

sched: Fix UP build breakage

2010-11-23T09:29:07+00:00

The recent cgroup-scheduling rework caused a UP build problem.

Cc: Paul Turner 
Signed-off-by: Peter Zijlstra 
LKML-Reference: 
Signed-off-by: Ingo Molnar

sched: Allow update_cfs_load() to update global load

2010-11-18T12:27:50+00:00

Refactor the global load updates from update_shares_cpu() so that
update_cfs_load() can update global load when it is more than ~10%
out of sync.

The new global_load parameter allows us to force an update, regardless of
the error factor so that we can synchronize w/ update_shares().

Signed-off-by: Paul Turner 
Signed-off-by: Peter Zijlstra 
LKML-Reference: <20101115234938.377473595@google.com>
Signed-off-by: Ingo Molnar

sched: Implement demand based update_cfs_load()

2010-11-18T12:27:49+00:00

When the system is busy, dilation of rq->next_balance makes lb->update_shares()
insufficiently frequent for threads which don't sleep (no dequeue/enqueue
updates).  Adjust for this by making demand based updates based on the
accumulation of execution time sufficient to wrap our averaging window.

Signed-off-by: Paul Turner 
Signed-off-by: Peter Zijlstra 
LKML-Reference: <20101115234938.291159744@google.com>
Signed-off-by: Ingo Molnar

sched: Update shares on idle_balance

2010-11-18T12:27:49+00:00

Since shares updates are no longer expensive and effectively local, update them
at idle_balance().  This allows us to more quickly redistribute shares to
another cpu when our load becomes idle.

Signed-off-by: Paul Turner 
Signed-off-by: Peter Zijlstra 
LKML-Reference: <20101115234938.204191702@google.com>
Signed-off-by: Ingo Molnar