Commit Graph

180 Commits

Author SHA1 Message Date
Peter Zijlstra 2070ee01d3 sched: cleanup old and rarely used 'debug' features.
TREE_AVG and APPROX_AVG are initial task placement policies that have been
disabled for a long while.. time to remove them.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
CC: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-03-21 16:43:47 +01:00
Ingo Molnar 74e3cd7f48 sched: retune wake granularity
reduce wake-up granularity for better interactivity.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-03-19 04:27:53 +01:00
Ingo Molnar 4ae7d5cefd sched: improve affine wakeups
improve affine wakeups. Maintain the 'overlap' metric based on CFS's
sum_exec_runtime - which means the amount of time a task executes
after it wakes up some other task.

Use the 'overlap' for the wakeup decisions: if the 'overlap' is short,
it means there's strong workload coupling between this task and the
woken up task. If the 'overlap' is large then the workload is decoupled
and the scheduler will move them to separate CPUs more easily.

( Also slightly move the preempt_check within try_to_wake_up() - this has
  no effect on functionality but allows 'early wakeups' (for still-on-rq
  tasks) to be correctly accounted as well.)

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-03-19 04:27:53 +01:00
Ingo Molnar f48273860e sched: clean up wakeup balancing, code flow
Clean up the code flow. No code changed:

kernel/sched.o:

   text	   data	    bss	    dec	    hex	filename
  42521	   2858	    232	  45611	   b22b	sched.o.before
  42521	   2858	    232	  45611	   b22b	sched.o.after

md5:
   09b31c44e9aff8666f72773dc433e2df  sched.o.before.asm
   09b31c44e9aff8666f72773dc433e2df  sched.o.after.asm

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-03-19 04:27:53 +01:00
Ingo Molnar ac192d3921 sched: clean up wakeup balancing, rename variables
rename 'cpu' to 'prev_cpu'. No code changed:

kernel/sched.o:

   text	   data	    bss	    dec	    hex	filename
  42521	   2858	    232	  45611	   b22b	sched.o.before
  42521	   2858	    232	  45611	   b22b	sched.o.after

md5:
   09b31c44e9aff8666f72773dc433e2df  sched.o.before.asm
   09b31c44e9aff8666f72773dc433e2df  sched.o.after.asm

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-03-19 04:27:52 +01:00
Ingo Molnar 098fb9db2c sched: clean up wakeup balancing, move wake_affine()
split out the affine-wakeup bits.

No code changed:

kernel/sched.o:

   text	   data	    bss	    dec	    hex	filename
  42521	   2858	    232	  45611	   b22b	sched.o.before
  42521	   2858	    232	  45611	   b22b	sched.o.after

md5:
   9d76738f1272aa82f0b7affd2f51df6b  sched.o.before.asm
   09b31c44e9aff8666f72773dc433e2df  sched.o.after.asm

(the md5's changed because stack slots changed and some registers
get scheduled by gcc in a different order - but otherwise the before
and after assembly is instruction for instruction equivalent.)

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-03-19 04:27:52 +01:00
Ingo Molnar 6a6029b8ce sched: simplify sched_slice()
Use the existing calc_delta_mine() calculation for sched_slice(). This
saves a divide and simplifies the code because we share it with the
other /cfs_rq->load users.

It also improves code size:

      text    data     bss     dec     hex filename
     42659    2740     144   45543    b1e7 sched.o.before
     42093    2740     144   44977    afb1 sched.o.after

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
2008-03-15 03:02:50 +01:00
Ingo Molnar e22ecef1d2 sched: fix fair sleepers
Fair sleepers need to scale their latency target down by runqueue
weight. Otherwise busy systems will gain ever larger sleep bonus.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
2008-03-15 03:02:50 +01:00
Peter Zijlstra aa2ac25229 sched: fix overload performance: buddy wakeups
Currently we schedule to the leftmost task in the runqueue. When the
runtimes are very short because of some server/client ping-pong,
especially in over-saturated workloads, this will cycle through all
tasks trashing the cache.

Reduce cache trashing by keeping dependent tasks together by running
newly woken tasks first. However, by not running the leftmost task first
we could starve tasks because the wakee can gain unlimited runtime.

Therefore we only run the wakee if its within a small
(wakeup_granularity) window of the leftmost task. This preserves
fairness, but does alternate server/client task groups.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-03-15 03:02:50 +01:00
Peter Zijlstra 3fe69747da sched: min_vruntime fix
Current min_vruntime tracking is incorrect and will cause serious
problems when we don't run the leftmost task for some reason.

min_vruntime does two things; 1) it's used to determine a forward
direction when the u64 vruntime wraps, 2) it's used to track the
leftmost vruntime to position newly enqueued tasks from.

The current logic advances min_vruntime whenever the current task's
vruntime advance. Because the current task may pass the leftmost task
still waiting we're failing the second goal. This causes new tasks to be
placed too far ahead and thus penalizes their runtime.

Fix this by making min_vruntime the min_vruntime of the waiting tasks by
tracking it in enqueue/dequeue, and compare against current's vruntime
to obtain the absolute minimum when placing new tasks.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-03-15 03:02:49 +01:00
Peter Zijlstra 810b38179e sched: retain vruntime
Kei Tokunaga reported an interactivity problem when moving tasks
between control groups.

Tasks would retain their old vruntime when moved between groups, this
can cause funny lags. Re-set the vruntime on group move to fit within
the new tree.

Reported-by: Kei Tokunaga <tokunaga.keiich@jp.fujitsu.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-03-07 16:42:59 +01:00
Peter Zijlstra 62fb185130 sched: revert load_balance_monitor() changes
The following commits cause a number of regressions:

  commit 58e2d4ca58
  Author: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
  Date:   Fri Jan 25 21:08:00 2008 +0100
  sched: group scheduling, change how cpu load is calculated

  commit 6b2d770026
  Author: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
  Date:   Fri Jan 25 21:08:00 2008 +0100
  sched: group scheduler, fix fairness of cpu bandwidth allocation for task groups

Namely:
 - very frequent wakeups on SMP, reported by PowerTop users.
 - cacheline trashing on (large) SMP
 - some latencies larger than 500ms

While there is a mergeable patch to fix the latter, the former issues
are not fixable in a manner suitable for .25 (we're at -rc3 now).

Hence we revert them and try again in v2.6.26.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
CC: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Tested-by: Alexey Zaytsev <alexey.zaytsev@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-03-04 17:54:06 +01:00
Ingo Molnar 7eee3e677d sched: clean up __pick_last_entity() a bit
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-02-25 16:34:17 +01:00
Balbir Singh 70eee74b70 sched: remove duplicate code from sched_fair.c
pick_task_entity() duplicates existing code. This functionality can be
easily obtained using rb_last(). Avoid code duplication by using rb_last().

Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-02-25 16:34:17 +01:00
Peter Zijlstra ef9884e6f2 sched: let +nice tasks have smaller impact
Michel Dänzr has bisected an interactivity problem with
plus-reniced tasks back to this commit:

 810e95ccd5 is first bad commit
 commit 810e95ccd5
 Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
 Date:   Mon Oct 15 17:00:14 2007 +0200

 sched: another wakeup_granularity fix

      unit mis-match: wakeup_gran was used against a vruntime

fix this by assymetrically scaling the vtime of positive reniced
tasks.

Bisected-by: Michel Dänzer <michel@tungstengraphics.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-31 22:45:22 +01:00
Srivatsa Vaddagiri 296825cbe1 sched: fix high wake up latencies with FAIR_USER_SCHED
The reason why we are getting better wakeup latencies for
!FAIR_USER_SCHED is because of this snippet of code in place_entity():

	if (!initial) {
		/* sleeps upto a single latency don't count. */
		if (sched_feat(NEW_FAIR_SLEEPERS) && entity_is_task(se))
						     ^^^^^^^^^^^^^^^^^^
			vruntime -= sysctl_sched_latency;

		/* ensure we never gain time by being placed backwards. */
		vruntime = max_vruntime(se->vruntime, vruntime);
	}

NEW_FAIR_SLEEPERS feature gives credit for sleeping only to tasks and
not group-level entities. With the patch attached, I could see that
wakeup latencies with FAIR_USER_SCHED are restored to the same level as
!FAIR_USER_SCHED.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-31 22:45:22 +01:00
Arjan van de Ven 6d082592b6 sched: keep total / count stats in addition to the max for
Right now, the linux kernel (with scheduler statistics enabled) keeps track
of the maximum time a process is waiting to be scheduled. While the maximum
is a very useful metric, tracking average and total is equally useful
(at least for latencytop) to figure out the accumulated effect of scheduler
delays. The accumulated effect is important to judge the performance impact
of scheduler tuning/behavior.

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:35 +01:00
Peter Zijlstra 5973e5b954 sched: fix: don't take a mutex from interrupt context
print_cfs_stats is callable from interrupt context (sysrq), hence it should
not take mutexes. Change it to use RCU since the task group data is RCU
freed anyway.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:34 +01:00
Arjan van de Ven 9745512ce7 sched: latencytop support
LatencyTOP kernel infrastructure; it measures latencies in the
scheduler and tracks it system wide and per process.

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:34 +01:00
Peter Zijlstra 8f4d37ec07 sched: high-res preemption tick
Use HR-timers (when available) to deliver an accurate preemption tick.

The regular scheduler tick that runs at 1/HZ can be too coarse when nice
level are used. The fairness system will still keep the cpu utilisation 'fair'
by then delaying the task that got an excessive amount of CPU time but try to
minimize this by delivering preemption points spot-on.

The average frequency of this extra interrupt is sched_latency / nr_latency.
Which need not be higher than 1/HZ, its just that the distribution within the
sched_latency period is important.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:29 +01:00
Steven Rostedt cb46984504 sched: RT-balance, add new methods to sched_class
Dmitry Adamushko found that the current implementation of the RT
balancing code left out changes to the sched_setscheduler and
rt_mutex_setprio.

This patch addresses this issue by adding methods to the schedule classes
to handle being switched out of (switched_from) and being switched into
(switched_to) a sched_class. Also a method for changing of priorities
is also added (prio_changed).

This patch also removes some duplicate logic between rt_mutex_setprio and
sched_setscheduler.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:22 +01:00
Peter Zijlstra 4bf0b77158 sched: remove do_div() from __sched_slice()
Yanmin Zhang noticed a nice optimization:

  p = l * nr / nl, nl = l/g -> p = g * nr

which eliminates a do_div() from __sched_period().

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:21 +01:00
Dmitry Adamushko 9ec3b77e11 sched: no need for 'affine wakeup' balancing
No need to do a check for 'affine wakeup and passive balancing possibilities'
in select_task_rq_fair() when task_cpu(p) == this_cpu.

I guess, this part got missed upon introduction of per-sched_class
select_task_rq() in try_to_wake_up().

Signed-off-by: Dmitry Adamushko <dmitry.adamushko@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:21 +01:00
Gregory Haskins e7693a362e sched: de-SCHED_OTHER-ize the RT path
The current wake-up code path tries to determine if it can optimize the
wake-up to "this_cpu" by computing load calculations.  The problem is that
these calculations are only relevant to SCHED_OTHER tasks where load is king.
For RT tasks, priority is king.  So the load calculation is completely wasted
bandwidth.

Therefore, we create a new sched_class interface to help with
pre-wakeup routing decisions and move the load calculation as a function
of CFS task's class.

Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:09 +01:00
Srivatsa Vaddagiri 6b2d770026 sched: group scheduler, fix fairness of cpu bandwidth allocation for task groups
The current load balancing scheme isn't good enough for precise
group fairness.

For example: on a 8-cpu system, I created 3 groups as under:

	a = 8 tasks (cpu.shares = 1024)
	b = 4 tasks (cpu.shares = 1024)
	c = 3 tasks (cpu.shares = 1024)

a, b and c are task groups that have equal weight. We would expect each
of the groups to receive 33.33% of cpu bandwidth under a fair scheduler.

This is what I get with the latest scheduler git tree:

Signed-off-by: Ingo Molnar <mingo@elte.hu>
--------------------------------------------------------------------------------
Col1  | Col2    | Col3  |  Col4
------|---------|-------|-------------------------------------------------------
a     | 277.676 | 57.8% | 54.1%  54.1%  54.1%  54.2%  56.7%  62.2%  62.8% 64.5%
b     | 116.108 | 24.2% | 47.4%  48.1%  48.7%  49.3%
c     |  86.326 | 18.0% | 47.5%  47.9%  48.5%
--------------------------------------------------------------------------------

Explanation of o/p:

Col1 -> Group name
Col2 -> Cumulative execution time (in seconds) received by all tasks of that
	group in a 60sec window across 8 cpus
Col3 -> CPU bandwidth received by the group in the 60sec window, expressed in
        percentage. Col3 data is derived as:
		Col3 = 100 * Col2 / (NR_CPUS * 60)
Col4 -> CPU bandwidth received by each individual task of the group.
		Col4 = 100 * cpu_time_recd_by_task / 60

[I can share the test case that produces a similar o/p if reqd]

The deviation from desired group fairness is as below:

	a = +24.47%
	b = -9.13%
	c = -15.33%

which is quite high.

After the patch below is applied, here are the results:

--------------------------------------------------------------------------------
Col1  | Col2    | Col3  |  Col4
------|---------|-------|-------------------------------------------------------
a     | 163.112 | 34.0% | 33.2%  33.4%  33.5%  33.5%  33.7%  34.4%  34.8% 35.3%
b     | 156.220 | 32.5% | 63.3%  64.5%  66.1%  66.5%
c     | 160.653 | 33.5% | 85.8%  90.6%  91.4%
--------------------------------------------------------------------------------

Deviation from desired group fairness is as below:

	a = +0.67%
	b = -0.83%
	c = +0.17%

which is far better IMO. Most of other runs have yielded a deviation within
+-2% at the most, which is good.

Why do we see bad (group) fairness with current scheuler?
=========================================================

Currently cpu's weight is just the summation of individual task weights.
This can yield incorrect results. For ex: consider three groups as below
on a 2-cpu system:

	CPU0	CPU1
---------------------------
	A (10)  B(5)
		C(5)
---------------------------

Group A has 10 tasks, all on CPU0, Group B and C have 5 tasks each all
of which are on CPU1. Each task has the same weight (NICE_0_LOAD =
1024).

The current scheme would yield a cpu weight of 10240 (10*1024) for each cpu and
the load balancer will think both CPUs are perfectly balanced and won't
move around any tasks. This, however, would yield this bandwidth:

	A = 50%
	B = 25%
	C = 25%

which is not the desired result.

What's changing in the patch?
=============================

	- How cpu weights are calculated when CONFIF_FAIR_GROUP_SCHED is
	  defined (see below)
	- API Change
		- Two tunables introduced in sysfs (under SCHED_DEBUG) to
		  control the frequency at which the load balance monitor
		  thread runs.

The basic change made in this patch is how cpu weight (rq->load.weight) is
calculated. Its now calculated as the summation of group weights on a cpu,
rather than summation of task weights. Weight exerted by a group on a
cpu is dependent on the shares allocated to it and also the number of
tasks the group has on that cpu compared to the total number of
(runnable) tasks the group has in the system.

Let,
	W(K,i)  = Weight of group K on cpu i
	T(K,i)  = Task load present in group K's cfs_rq on cpu i
	T(K)    = Total task load of group K across various cpus
	S(K) 	= Shares allocated to group K
	NRCPUS	= Number of online cpus in the scheduler domain to
	 	  which group K is assigned.

Then,
	W(K,i) = S(K) * NRCPUS * T(K,i) / T(K)

A load balance monitor thread is created at bootup, which periodically
runs and adjusts group's weight on each cpu. To avoid its overhead, two
min/max tunables are introduced (under SCHED_DEBUG) to control the rate
at which it runs.

Fixes from: Peter Zijlstra <a.p.zijlstra@chello.nl>

- don't start the load_balance_monitor when there is only a single cpu.
- rename the kthread because its currently longer than TASK_COMM_LEN

Signed-off-by: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:00 +01:00
Srivatsa Vaddagiri 58e2d4ca58 sched: group scheduling, change how cpu load is calculated
This patch changes how the cpu load exerted by fair_sched_class tasks
is calculated. Load exerted by fair_sched_class tasks on a cpu is now
a summation of the group weights, rather than summation of task weights.
Weight exerted by a group on a cpu is dependent on the shares allocated
to it.

This version of patch has a minor impact on code size, but should have
no runtime/functional impact for !CONFIG_FAIR_GROUP_SCHED.

Signed-off-by: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:00 +01:00
Srivatsa Vaddagiri ec2c507fe8 sched: group scheduling, minor fixes
Minor bug fixes for the group scheduler:

- Use a mutex to serialize add/remove of task groups and also when
  changing shares of a task group. Use the same mutex when printing
  cfs_rq debugging stats for various task groups.

- Use list_for_each_entry_rcu in for_each_leaf_cfs_rq macro (when
  walking task group list)

Signed-off-by: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:07:59 +01:00
Ingo Molnar 6cbf1c126c sched: do not hurt SCHED_BATCH on wakeup
measurements by Yanmin Zhang have shown that SCHED_BATCH tasks benefit
if they run the same place_entity() logic as SCHED_OTHER tasks - so
uniformize behavior in this area.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-12-18 15:21:13 +01:00
Ingo Molnar db292ca302 sched: default to more agressive yield for SCHED_BATCH tasks
do more agressive yield for SCHED_BATCH tuned tasks: they are all
about throughput anyway. This allows a gentler migration path for
any apps that relied on stronger yield.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-12-04 17:04:39 +01:00
Srivatsa Vaddagiri d842de871c sched: cpu accounting controller (V2)
Commit cfb5285660 removed a useful feature for
us, which provided a cpu accounting resource controller.  This feature would be
useful if someone wants to group tasks only for accounting purpose and doesnt
really want to exercise any control over their cpu consumption.

The patch below reintroduces the feature. It is based on Paul Menage's
original patch (Commit 62d0df6406), with
these differences:

        - Removed load average information. I felt it needs more thought (esp
	  to deal with SMP and virtualized platforms) and can be added for
	  2.6.25 after more discussions.
        - Convert group cpu usage to be nanosecond accurate (as rest of the cfs
	  stats are) and invoke cpuacct_charge() from the respective scheduler
	  classes
	- Make accounting scalable on SMP systems by splitting the usage
	  counter to be per-cpu
	- Move the code from kernel/cpu_acct.c to kernel/sched.c (since the
	  code is not big enough to warrant a new file and also this rightly
	  needs to live inside the scheduler. Also things like accessing
	  rq->lock while reading cpu usage becomes easier if the code lived in
	  kernel/sched.c)

The patch also modifies the cpu controller not to provide the same accounting
information.

Tested-by: Balbir Singh <balbir@linux.vnet.ibm.com>

 Tested the patches on top of 2.6.24-rc3. The patches work fine. Ran
 some simple tests like cpuspin (spin on the cpu), ran several tasks in
 the same group and timed them. Compared their time stamps with
 cpuacct.usage.

Signed-off-by: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-12-02 20:04:49 +01:00
Zou Nan hai 722aab0c3b sched: fix minimum granularity tunings
increase the default minimum granularity some more - this gives us
more performance in aim7 benchmarks.

also correct some comments: we scale with ilog(ncpus) + 1.

Signed-off-by: Zou Nan hai <nanhai.zou@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-11-26 21:21:49 +01:00
Adrian Bunk 518b22e990 sched: make sched_nr_latency static
sched_nr_latency can now become static.

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-11-15 20:57:40 +01:00
Srivatsa Vaddagiri 3c90e6e99b sched: fix copy_namespace() <-> sched_fork() dependency in do_fork
Sukadev Bhattiprolu reported a kernel crash with control groups.
There are couple of problems discovered by Suka's test:

- The test requires the cgroup filesystem to be mounted with
  atleast the cpu and ns options (i.e both namespace and cpu 
  controllers are active in the same hierarchy). 

	# mkdir /dev/cpuctl
	# mount -t cgroup -ocpu,ns none cpuctl
	(or simply)
	# mount -t cgroup none cpuctl -> Will activate all controllers
					 in same hierarchy.

- The test invokes clone() with CLONE_NEWNS set. This causes a a new child
  to be created, also a new group (do_fork->copy_namespaces->ns_cgroup_clone->
  cgroup_clone) and the child is attached to the new group (cgroup_clone->
  attach_task->sched_move_task). At this point in time, the child's scheduler 
  related fields are uninitialized (including its on_rq field, which it has
  inherited from parent). As a result sched_move_task thinks its on
  runqueue, when it isn't.

  As a solution to this problem, I moved sched_fork() call, which
  initializes scheduler related fields on a new task, before
  copy_namespaces(). I am not sure though whether moving up will
  cause other side-effects. Do you see any issue?

- The second problem exposed by this test is that task_new_fair()
  assumes that parent and child will be part of the same group (which 
  needn't be as this test shows). As a result, cfs_rq->curr can be NULL
  for the child.

  The solution is to test for curr pointer being NULL in
  task_new_fair().

With the patch below, I could run ns_exec() fine w/o a crash.

Reported-by: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Signed-off-by: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-11-09 22:39:39 +01:00
Ingo Molnar 502d26b524 sched: clean up the wakeup preempt check, #2
clean up the preemption check to not use unnecessary 64-bit
variables. This improves code size:

   text    data     bss     dec     hex filename
  44227    3326      36   47589    b9e5 sched.o.before
  44201    3326      36   47563    b9cb sched.o.after

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-11-09 22:39:39 +01:00
Ingo Molnar 77d9cc44b5 sched: clean up the wakeup preempt check
clean up the wakeup preemption check. No code changed:

   text    data     bss     dec     hex filename
  44227    3326      36   47589    b9e5 sched.o.before
  44227    3326      36   47589    b9e5 sched.o.after

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-11-09 22:39:39 +01:00
Ingo Molnar 8bc6767acb sched: wakeup preemption fix
wakeup preemption fix: do not make it dependent on p->prio.
Preemption purely depends on ->vruntime.

This improves preemption in mixed-nice-level workloads.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-11-09 22:39:39 +01:00
Ingo Molnar 3e3e13f399 sched: remove PREEMPT_RESTRICT
remove PREEMPT_RESTRICT. (this is a separate commit so that any
regression related to the removal itself is bisectable)

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-11-09 22:39:39 +01:00
Ingo Molnar 19978ca610 sched: reintroduce SMP tunings again
Yanmin Zhang reported an aim7 regression and bisected it down to:

 |  commit 38ad464d41
 |  Author: Ingo Molnar <mingo@elte.hu>
 |  Date:   Mon Oct 15 17:00:02 2007 +0200
 |
 |     sched: uniform tunings
 |
 |     use the same defaults on both UP and SMP.

fix this by reintroducing similar SMP tunings again. This resolves
the regression.

(also update the comments to match the ilog2(nr_cpus) tuning effect)

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-11-09 22:39:38 +01:00
Peter Zijlstra b2be5e96dc sched: reintroduce the sched_min_granularity tunable
we lost the sched_min_granularity tunable to a clever optimization
that uses the sched_latency/min_granularity ratio - but the ratio
is quite unintuitive to users and can also crash the kernel if the
ratio is set to 0. So reintroduce the min_granularity tunable,
while keeping the ratio maintained internally.

no functionality changed.

[ mingo@elte.hu: some fixlets. ]

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-11-09 22:39:37 +01:00
Peter Zijlstra 2cb8600e6b sched: documentation: place_entity() comments
Add a few comments to place_entity(). No code changed.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-11-09 22:39:37 +01:00
Peter Zijlstra 10b777246c sched: fix vslice
vslice was missing a factor NICE_0_LOAD, as weight is in
weight*NICE_0_LOAD units.

the effect of this bug was larger initial slices and
thus latency-noisier forks.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-11-09 22:39:37 +01:00
Ingo Molnar 8eb172d941 sched: fix style of swap() macro in kernel/sched_fair.c
fix style of swap() macro in kernel/sched_fair.c.

( this macro should eventually move to a general header, as ext3 uses
  a similar construct too. )

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-10-29 21:18:11 +01:00
Peter Williams 681f3e6854 sched: isolate SMP balancing code a bit more
At the moment, a lot of load balancing code that is irrelevant to non
SMP systems gets included during non SMP builds.

This patch addresses this issue and reduces the binary size on non
SMP systems:

   text    data     bss     dec     hex filename
  10983      28    1192   12203    2fab sched.o.before
  10739      28    1192   11959    2eb7 sched.o.after

Signed-off-by: Peter Williams <pwil3058@bigpond.net.au>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-10-24 18:23:51 +02:00
Peter Williams e1d1484f72 sched: reduce balance-tasks overhead
At the moment, balance_tasks() provides low level functionality for both
  move_tasks() and move_one_task() (indirectly) via the load_balance()
function (in the sched_class interface) which also provides dual
functionality.  This dual functionality complicates the interfaces and
internal mechanisms and makes the run time overhead of operations that
are called with two run queue locks held.

This patch addresses this issue and reduces the overhead of these
operations.

Signed-off-by: Peter Williams <pwil3058@bigpond.net.au>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-10-24 18:23:51 +02:00
Srivatsa Vaddagiri b9dca1e0fc sched: fix new task startup crash
Child task may be added on a different cpu that the one on which parent
is running. In which case, task_new_fair() should check whether the new
born task's parent entity should be added as well on the cfs_rq.

Patch below fixes the problem in task_new_fair.

This could fix the put_prev_task_fair() crashes reported.

Reported-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Reported-by: Andy Whitcroft <apw@shadowen.org>
Signed-off-by: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-10-17 16:55:11 +02:00
Ingo Molnar da84d96176 sched: reintroduce cache-hot affinity
reintroduce a simplified version of cache-hot/cold scheduling
affinity. This improves performance with certain SMP workloads,
such as sysbench.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-10-15 17:00:18 +02:00
Ingo Molnar e5f32a3856 sched: speed up context-switches a bit
speed up context-switches a bit by not clearing p->exec_start.

(as a side-effect, this also makes p->exec_start a universal timestamp
available to cache-hot estimations.)

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-10-15 17:00:18 +02:00
Ingo Molnar 91c234b4e3 sched: do not wakeup-preempt with SCHED_BATCH tasks
do not wakeup-preempt with SCHED_BATCH tasks, their preemption
is batched too, driven by the tick.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-10-15 17:00:18 +02:00
Ingo Molnar d274a4cee1 sched: update comment
update comment: clarify time-slices and remove obsolete tuning detail.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-10-15 17:00:14 +02:00
Mike Galbraith 95938a35c5 sched: prevent wakeup over-scheduling
Prevent wakeup over-scheduling.  Once a task has been preempted by a
task of the same or lower priority, it becomes ineligible for repeated
preemption by same until it has been ticked, or slept.  Instead, the
task is marked for preemption at the next tick.  Tasks of higher
priority still preempt immediately.

Signed-off-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-10-15 17:00:14 +02:00