Its a source of fail, also, now that cpu_power is dynamical,
its a waste of time.

before:
<idle>-0   [000]   132.877936: find_busiest_group: avg_load: 0 group_load: 8241 power: 1

after:
bash-1689  [001]   137.862151: find_busiest_group: avg_load: 10636288 group_load: 10387 power: 1

[ v2: build fix from From: Andreas Herrmann ]
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Tested-by: NAndreas Herrmann <andreas.herrmann3@amd.com>
Acked-by: NAndreas Herrmann <andreas.herrmann3@amd.com>
Acked-by: NGautham R Shenoy <ego@in.ibm.com>
Cc: Balbir Singh <balbir@in.ibm.com>
LKML-Reference: <20090901083826.425896304@chello.nl>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

sgs.group_capacity can now be 0, if for some reason
group->__cpu_power happens to be less than SCHED_LOAD_SCALE/2.

In that case, we need the following fix to make it work for
update_sd_power_savings_stats(). That's because both
sum_nr_running and group_capacity are unsigned longs.

Cc: Gautham R Shenoy <ego@in.ibm.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Andreas Herrmann <andreas.herrmann3@amd.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

When the capacity drops low, we want to migrate load away.
Allow the load-balancer to remove all tasks when we hit rock
bottom.
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Tested-by: NAndreas Herrmann <andreas.herrmann3@amd.com>
Acked-by: NAndreas Herrmann <andreas.herrmann3@amd.com>
Acked-by: NGautham R Shenoy <ego@in.ibm.com>
Cc: Balbir Singh <balbir@in.ibm.com>
LKML-Reference: <20090901083826.342231003@chello.nl>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Keep an average on the amount of time spend on RT tasks and use
that fraction to scale down the cpu_power for regular tasks.
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Tested-by: NAndreas Herrmann <andreas.herrmann3@amd.com>
Acked-by: NAndreas Herrmann <andreas.herrmann3@amd.com>
Acked-by: NGautham R Shenoy <ego@in.ibm.com>
Cc: Balbir Singh <balbir@in.ibm.com>
LKML-Reference: <20090901083826.287778431@chello.nl>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Recompute the cpu_power for each cpu during load-balance.
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Tested-by: NAndreas Herrmann <andreas.herrmann3@amd.com>
Acked-by: NAndreas Herrmann <andreas.herrmann3@amd.com>
Acked-by: NGautham R Shenoy <ego@in.ibm.com>
Cc: Balbir Singh <balbir@in.ibm.com>
LKML-Reference: <20090901083826.162033479@chello.nl>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

The idea is that multi-threading a core yields more work
capacity than a single thread, provide a way to express a
static gain for threads.
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Tested-by: NAndreas Herrmann <andreas.herrmann3@amd.com>
Acked-by: NAndreas Herrmann <andreas.herrmann3@amd.com>
Acked-by: NGautham R Shenoy <ego@in.ibm.com>
Cc: Balbir Singh <balbir@in.ibm.com>
LKML-Reference: <20090901083826.073345955@chello.nl>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

In order to prepare for a more dynamic cpu_power, update the
group sum while walking the sched domains during load-balance.
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Tested-by: NAndreas Herrmann <andreas.herrmann3@amd.com>
Acked-by: NAndreas Herrmann <andreas.herrmann3@amd.com>
Acked-by: NGautham R Shenoy <ego@in.ibm.com>
Cc: Balbir Singh <balbir@in.ibm.com>
LKML-Reference: <20090901083825.985050292@chello.nl>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Do the placement thing using SD flags.
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Tested-by: NAndreas Herrmann <andreas.herrmann3@amd.com>
Acked-by: NAndreas Herrmann <andreas.herrmann3@amd.com>
Acked-by: NGautham R Shenoy <ego@in.ibm.com>
Cc: Balbir Singh <balbir@in.ibm.com>
LKML-Reference: <20090901083825.897028974@chello.nl>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

cpu_power is supposed to be a representation of the process
capacity of the cpu, not a value to randomly tweak in order to
affect placement.

Remove the placement hacks.
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Tested-by: NAndreas Herrmann <andreas.herrmann3@amd.com>
Acked-by: NAndreas Herrmann <andreas.herrmann3@amd.com>
Acked-by: NGautham R Shenoy <ego@in.ibm.com>
Cc: Balbir Singh <balbir@in.ibm.com>
LKML-Reference: <20090901083825.810860576@chello.nl>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

For counting how long an application has been waiting for
(disk) IO, there currently is only the HZ sample driven
information available, while for all other counters in this
class, a high resolution version is available via
CONFIG_SCHEDSTATS.

In order to make an improved bootchart tool possible, we also
need a higher resolution version of the iowait time.

This patch below adds this scheduler statistic to the kernel.
Signed-off-by: NArjan van de Ven <arjan@linux.intel.com>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <4A64B813.1080506@linux.intel.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

... so that it does not share a common name with a function
within the same scope.
Signed-off-by: NAnirban Sinha <asinha@zeugmasystems.com>
LKML-Reference: <DDFD17CC94A9BD49A82147DDF7D545C501EA98A6@exchange.ZeugmaSystems.local>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

When re-computing the shares for each task group's cpu
representation we need the ratio of weight on each cpu vs the
total weight of the sched domain.

Since load-balancing is loosely (read not) synchronized, the
weight of individual cpus can change between doing the sum and
calculating the ratio.

The previous patch dealt with only one of the race scenarios,
this patch side steps them all by saving a snapshot of all the
individual cpu weights, thereby always working on a consistent
set.
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: torvalds@linux-foundation.org
Cc: jes@sgi.com
Cc: jens.axboe@oracle.com
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Arjan van de Ven <arjan@infradead.org>
Cc: Yinghai Lu <yinghai@kernel.org>
LKML-Reference: <1251371336.18584.77.camel@twins>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Patch a5004278 (sched: Fix
cgroup smp fairness) introduced the possibility of a
divide-by-zero because load-balancing is not synchronized
between sched_domains.

This can cause the state of cpus to change between the first
and second loop over the sched domain in tg_shares_up().
Reported-by: NYinghai Lu <yinghai@kernel.org>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Jes Sorensen <jes@sgi.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
LKML-Reference: <1250855934.7538.30.camel@twins>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Replace for loop with the macro for_each_class to cleanup.
Signed-off-by: NHiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>
LKML-Reference: <4A8A277D.4090304@ct.jp.nec.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Signed-off-by: NAndreas Herrmann <andreas.herrmann3@amd.com>
Cc: Peter Zijlstra <peterz@infradead.org>
LKML-Reference: <20090818110229.GM29515@alberich.amd.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

... to further strip down __build_sched_domains().
Signed-off-by: NAndreas Herrmann <andreas.herrmann3@amd.com>
Cc: Peter Zijlstra <peterz@infradead.org>
LKML-Reference: <20090818110111.GL29515@alberich.amd.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

For the sake of completeness.
Now all calls to init_sched_build_groups() are contained in
build_sched_groups().
Signed-off-by: NAndreas Herrmann <andreas.herrmann3@amd.com>
Cc: Peter Zijlstra <peterz@infradead.org>
LKML-Reference: <20090818110013.GK29515@alberich.amd.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

... to further strip down __build_sched_domains().
Signed-off-by: NAndreas Herrmann <andreas.herrmann3@amd.com>
Cc: Peter Zijlstra <peterz@infradead.org>
LKML-Reference: <20090818105928.GJ29515@alberich.amd.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

... to further strip down __build_sched_domains().
Signed-off-by: NAndreas Herrmann <andreas.herrmann3@amd.com>
Cc: Peter Zijlstra <peterz@infradead.org>
LKML-Reference: <20090818105838.GI29515@alberich.amd.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

... to further strip down __build_sched_domains().
Signed-off-by: NAndreas Herrmann <andreas.herrmann3@amd.com>
Cc: Peter Zijlstra <peterz@infradead.org>
LKML-Reference: <20090818105751.GH29515@alberich.amd.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

... to further strip down __build_sched_domains().
Signed-off-by: NAndreas Herrmann <andreas.herrmann3@amd.com>
Cc: Peter Zijlstra <peterz@infradead.org>
LKML-Reference: <20090818105703.GG29515@alberich.amd.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

... to further strip down __build_sched_domains().
Signed-off-by: NAndreas Herrmann <andreas.herrmann3@amd.com>
Cc: Peter Zijlstra <peterz@infradead.org>
LKML-Reference: <20090818105614.GF29515@alberich.amd.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

... to further strip down __build_sched_domains().
Signed-off-by: NAndreas Herrmann <andreas.herrmann3@amd.com>
Cc: Peter Zijlstra <peterz@infradead.org>
LKML-Reference: <20090818105455.GE29515@alberich.amd.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

... to further strip down __build_sched_domains().
Signed-off-by: NAndreas Herrmann <andreas.herrmann3@amd.com>
Cc: Peter Zijlstra <peterz@infradead.org>
LKML-Reference: <20090818105406.GD29515@alberich.amd.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Signed-off-by: NAndreas Herrmann <andreas.herrmann3@amd.com>
Cc: Peter Zijlstra <peterz@infradead.org>
LKML-Reference: <20090818105300.GC29515@alberich.amd.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Signed-off-by: NAndreas Herrmann <andreas.herrmann3@amd.com>
Cc: Peter Zijlstra <peterz@infradead.org>
LKML-Reference: <20090818105152.GB29515@alberich.amd.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Like sched_migrate_task(), set_cpus_allowed_ptr() should hold
onto the migration thread too.
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Reflect "active" cpus in the rq->rd->online field, instead of
the online_map.

The motivation is that things that use the root-domain code
(such as cpupri) only care about cpus classified as "active"
anyway. By synchronizing the root-domain state with the active
map, we allow several optimizations.

For instance, we can remove an extra cpumask_and from the
scheduler hotpath by utilizing rq->rd->online (since it is now
a cached version of cpu_active_map & rq->rd->span).
Signed-off-by: NGregory Haskins <ghaskins@novell.com>
Acked-by: NPeter Zijlstra <peterz@infradead.org>
Acked-by: NMax Krasnyansky <maxk@qualcomm.com>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20090730145723.25226.24493.stgit@dev.haskins.net>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

We currently have an explicit "needs_post" vtable method which
returns a stack variable for whether we should later run
post-schedule.  This leads to an awkward exchange of the
variable as it bubbles back up out of the context switch. Peter
Zijlstra observed that this information could be stored in the
run-queue itself instead of handled on the stack.

Therefore, we revert to the method of having context_switch
return void, and update an internal rq->post_schedule variable
when we require further processing.

In addition, we fix a race condition where we try to access
current->sched_class without holding the rq->lock.  This is
technically racy, as the sched-class could change out from
under us.  Instead, we reference the per-rq post_schedule
variable with the runqueue unlocked, but with preemption
disabled to see if we need to reacquire the rq->lock.

Finally, we clean the code up slightly by removing the #ifdef
CONFIG_SMP conditionals from the schedule() call, and implement
some inline helper functions instead.

This patch passes checkpatch, and rt-migrate.
Signed-off-by: NGregory Haskins <ghaskins@novell.com>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20090729150422.17691.55590.stgit@dev.haskins.net>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

The current method for pushing RT tasks after scheduling only
happens after a context switch. But we found cases where a task
is set up on a run queue to be pushed but the push never
happens because the schedule chooses the same task.

This bug was found with the help of Gregory Haskins and the use
of ftrace (trace_printk). It tooks several days for both of us
analyzing the code and the trace output to find this.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20090729042526.205923666@goodmis.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

When cgroup group scheduling is built in, skip some code paths
if we don't have any (but the root) cgroups configured.
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Commit ec4e0e2f ("fix
inconsistency when redistribute per-cpu tg->cfs_rq shares")
broke cgroup smp fairness.

In order to avoid starvation of newly placed tasks, we never
quite set the share of an empty cpu group-task to 0, but
instead we set it as if there's a single NICE-0 task present.

If however we actually set this in cfs_rq[cpu]->shares, that
means the total shares for that group will be slightly inflated
every time we balance, causing the observed unfairness.

Fix this by setting cfs_rq[cpu]->shares to 0 but actually
setting the effective weight of the related se to the inflated
number.
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1248696557.6987.1615.camel@twins>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

migration_init() returns the return value of the hotplug notifier. In
the success case this is NOTIFY_OK which is 1. initcall_debug
evaluates that as an error code because init calls are expected to
return 0 on success.
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

might_sleep() is called late-ish in cond_resched(), after the
need_resched()/preempt enabled/system running tests are
checked.

It's better to check the sleeps while atomic earlier and not
depend on some environment datas that reduce the chances to
detect a problem.

Also define cond_resched_*() helpers as macros, so that the
FILE/LINE reported in the sleeping while atomic warning
displays the real origin and not sched.h

Changes in v2:

 - Call __might_sleep() directly instead of might_sleep() which
   may call cond_resched()

 - Turn cond_resched() into a macro so that the file:line
   couple reported refers to the caller of cond_resched() and
   not __cond_resched() itself.

Changes in v3:

 - Also propagate this __might_sleep() pull up to
   cond_resched_lock() and cond_resched_softirq()
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1247725694-6082-6-git-send-email-fweisbec@gmail.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Add a preempt count base offset to compare against the current
preempt level count. It prepares to pull up the might_sleep
check from cond_resched() to cond_resched_lock() and
cond_resched_bh().

For these two helpers, we need to respectively ensure that once
we'll unlock the given spinlock / reenable local softirqs, we
will reach a sleepable state.
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
[ Move and rename preempt_count_equals() ]
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1247725694-6082-4-git-send-email-fweisbec@gmail.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Cover the off case for __might_sleep(), so that we avoid
#ifdefs in files that make use of it. Especially, this prepares
for the __might_sleep() pull up on cond_resched().
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1247725694-6082-3-git-send-email-fweisbec@gmail.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Remove the outdated comment from __cond_resched() related to
the now removed Big Kernel Semaphore.
Reported-by: NArnd Bergmann <arnd@arndb.de>
Reported-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1247725694-6082-2-git-send-email-fweisbec@gmail.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

The schedule() function is a loop that reschedules the current
task while the TIF_NEED_RESCHED flag is set:

void schedule(void)
{
need_resched:
	/* schedule code */
	if (need_resched())
		goto need_resched;
}

And cond_resched() repeat this loop:

do {
	add_preempt_count(PREEMPT_ACTIVE);
	schedule();
	sub_preempt_count(PREEMPT_ACTIVE);
} while(need_resched());

This loop is needless because schedule() already did the check
and nothing can set TIF_NEED_RESCHED between schedule() exit
and the loop check in need_resched().

Then remove this needless loop.
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
Acked-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1247725694-6082-1-git-send-email-fweisbec@gmail.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

The new load average code clears rq->calc_load_active on
CPU_ONLINE. That's wrong as the new onlined CPU might have got a
scheduler tick already and accounted the delta to the stale value of
the time we offlined the CPU.

Clear the value when we cleanup the dead CPU instead. 

Also move the update of the calc_load_update time for the newly online
CPU to CPU_UP_PREPARE to avoid that the CPU plays catch up with the
stale update time value.
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

Optimize cond_resched() by removing one conditional.

Currently cond_resched() checks system_state ==
SYSTEM_RUNNING in order to avoid scheduling before the
scheduler is running.

We can however, as per suggestion of Matt, use
PREEMPT_ACTIVE to accomplish that very same.
Suggested-by: NMatt Mackall <mpm@selenic.com>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: NMatt Mackall <mpm@selenic.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>