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  1. 28 10月, 2014 7 次提交
  3. 24 9月, 2014 2 次提交
  5. 19 9月, 2014 1 次提交
  7. 07 9月, 2014 1 次提交
    • X
      sched/deadline: Fix a precision problem in the microseconds range · 177ef2a6
      由 xiaofeng.yan 提交于 
      An overrun could happen in function start_hrtick_dl()
when a task with SCHED_DEADLINE runs in the microseconds
range.

For example, if a task with SCHED_DEADLINE has the following parameters:

  Task  runtime  deadline  period
   P1   200us     500us    500us

The deadline and period from task P1 are less than 1ms.

In order to achieve microsecond precision, we need to enable HRTICK feature
by the next command:

  PC#echo "HRTICK" > /sys/kernel/debug/sched_features
  PC#trace-cmd record -e sched_switch &
  PC#./schedtool -E -t 200000:500000:500000 -e ./test

The binary test is in an endless while(1) loop here.
Some pieces of trace.dat are as follows:

  <idle>-0   157.603157: sched_switch: :R ==> 2481:4294967295: test
  test-2481  157.603203: sched_switch:  2481:R ==> 0:120: swapper/2
  <idle>-0   157.605657: sched_switch:  :R ==> 2481:4294967295: test
  test-2481  157.608183: sched_switch:  2481:R ==> 2483:120: trace-cmd
  trace-cmd-2483 157.609656: sched_switch:2483:R==>2481:4294967295: test

We can get the runtime of P1 from the information above:

  runtime = 157.608183 - 157.605657
  runtime = 0.002526(2.526ms)

The correct runtime should be less than or equal to 200us at some point.

The problem is caused by a conditional judgment "delta > 10000"
in function start_hrtick_dl().

Because no hrtimer start up to control the rest of runtime
when the reset of runtime is less than 10us.

So the process will continue to run until tick-period is coming.

Move the code with the limit of the least time slice
from hrtick_start_fair() to hrtick_start() because the
EDF schedule class also needs this function in start_hrtick_dl().

To fix this problem, we call hrtimer_start() unconditionally in
start_hrtick_dl(), and make sure the scheduling slice won't be smaller
than 10us in hrtimer_start().
Signed-off-by: NXiaofeng Yan <xiaofeng.yan@huawei.com>
Reviewed-by: NLi Zefan <lizefan@huawei.com>
Acked-by: NJuri Lelli <juri.lelli@arm.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1409022941-5880-1-git-send-email-xiaofeng.yan@huawei.com
[ Massaged the changelog and the code. ]
Signed-off-by: NIngo Molnar <mingo@kernel.org>
      177ef2a6
  9. 28 8月, 2014 1 次提交
    • C
      percpu: Resolve ambiguities in __get_cpu_var/cpumask_var_t · 4ba29684
      由 Christoph Lameter 提交于 
      __get_cpu_var can paper over differences in the definitions of
cpumask_var_t and either use the address of the cpumask variable
directly or perform a fetch of the address of the struct cpumask
allocated elsewhere. This is important particularly when using per cpu
cpumask_var_t declarations because in one case we have an offset into
a per cpu area to handle and in the other case we need to fetch a
pointer from the offset.

This patch introduces a new macro

this_cpu_cpumask_var_ptr()

that is defined where cpumask_var_t is defined and performs the proper
actions. All use cases where __get_cpu_var is used with cpumask_var_t
are converted to the use of this_cpu_cpumask_var_ptr().
Signed-off-by: NChristoph Lameter <cl@linux.com>
Signed-off-by: NTejun Heo <tj@kernel.org>
      4ba29684
  11. 20 8月, 2014 1 次提交
    • K
      sched: Add wrapper for checking task_struct::on_rq · da0c1e65
      由 Kirill Tkhai 提交于 
      Implement task_on_rq_queued() and use it everywhere instead of
on_rq check. No functional changes.

The only exception is we do not use the wrapper in
check_for_tasks(), because it requires to export
task_on_rq_queued() in global header files. Next patch in series
would return it back, so we do not twist it from here to there.
Signed-off-by: NKirill Tkhai <ktkhai@parallels.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paul Turner <pjt@google.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Kirill Tkhai <tkhai@yandex.ru>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Nicolas Pitre <nicolas.pitre@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1408528052.23412.87.camel@tkhaiSigned-off-by: NIngo Molnar <mingo@kernel.org>
      da0c1e65
  13. 16 7月, 2014 2 次提交
  15. 05 6月, 2014 4 次提交
  17. 22 5月, 2014 2 次提交
  19. 07 5月, 2014 1 次提交
  21. 17 4月, 2014 1 次提交
  23. 11 3月, 2014 1 次提交
  25. 27 2月, 2014 2 次提交
    • J
      sched/deadline: Prevent rt_time growth to infinity · faa59937
      由 Juri Lelli 提交于 
      Kirill Tkhai noted:

  Since deadline tasks share rt bandwidth, we must care about
  bandwidth timer set. Otherwise rt_time may grow up to infinity
  in update_curr_dl(), if there are no other available RT tasks
  on top level bandwidth.

RT task were in fact throttled right after they got enqueued,
and never executed again (rt_time never again went below rt_runtime).

Peter then proposed to accrue DL execution on rt_time only when
rt timer is active, and proposed a patch (this patch is a slight
modification of that) to implement that behavior. While this
solves Kirill problem, it has a drawback.

Indeed, Kirill noted again:

  It looks we may get into a situation, when all CPU time is shared
  between RT and DL tasks:

  rt_runtime = n
  rt_period  = 2n

  | RT working, DL sleeping  | DL working, RT sleeping      |
  -----------------------------------------------------------
  | (1)     duration = n     | (2)     duration = n         | (repeat)
  |--------------------------|------------------------------|
  | (rt_bw timer is running) | (rt_bw timer is not running) |

  No time for fair tasks at all.

While this can happen during the first period, if rq is always backlogged,
RT tasks won't have the opportunity to execute anymore: rt_time reached
rt_runtime during (1), suppose after (2) RT is enqueued back, it gets
throttled since rt timer didn't fire, replenishment is from now on eaten up
by DL tasks that accrue their execution on rt_time (while rt timer is
active - we have an RT task waiting for replenishment). FAIR tasks are
not touched after this first period. Ok, this is not ideal, and the situation
is even worse!

What above (the nice case), practically never happens in reality, where
your rt timer is not aligned to tasks periods, tasks are in general not
periodic, etc.. Long story short, you always risk to overload your system.

This patch is based on Peter's idea, but exploits an additional fact:
if you don't have RT tasks enqueued, it makes little sense to continue
incrementing rt_time once you reached the upper limit (DL tasks have their
own mechanism for throttling).

This cures both problems:

 - no matter how many DL instances in the past, you'll have an rt_time
   slightly above rt_runtime when an RT task is enqueued, and from that
   point on (after the first replenishment), the task will normally execute;

 - you can still eat up all bandwidth during the first period, but not
   anymore after that, remember that DL execution will increment rt_time
   till the upper limit is reached.

The situation is still not perfect! But, we have a simple solution for now,
that limits how much you can jeopardize your system, as we keep working
towards the right answer: RT groups scheduled using deadline servers.
Reported-by: NKirill Tkhai <tkhai@yandex.ru>
Signed-off-by: NJuri Lelli <juri.lelli@gmail.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/20140225151515.617714e2f2cd6c558531ba61@gmail.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      faa59937
    • K
      sched/deadline: Cleanup RT leftovers from {inc/dec}_dl_migration · 3908ac13
      由 Kirill Tkhai 提交于 
      In deadline class we do not have group scheduling.

So, let's remove unnecessary

	X = X;

equations.
Signed-off-by: NKirill Tkhai <ktkhai@parallels.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@gmail.com>
Link: http://lkml.kernel.org/r/1393343543.4089.5.camel@tkhaiSigned-off-by: NIngo Molnar <mingo@kernel.org>
      3908ac13
  27. 22 2月, 2014 4 次提交
    • P
      sched: Remove some #ifdeffery · dc877341
      由 Peter Zijlstra 提交于 
      Remove a few gratuitous #ifdefs in pick_next_task*().

Cc: Ingo Molnar <mingo@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Juri Lelli <juri.lelli@gmail.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-nnzddp5c4fijyzzxxrwlxghf@git.kernel.orgSigned-off-by: NThomas Gleixner <tglx@linutronix.de>
      dc877341
    • P
      sched: Fix hotplug task migration · 3f1d2a31
      由 Peter Zijlstra 提交于 
      Dan Carpenter reported:

> kernel/sched/rt.c:1347 pick_next_task_rt() warn: variable dereferenced before check 'prev' (see line 1338)
> kernel/sched/deadline.c:1011 pick_next_task_dl() warn: variable dereferenced before check 'prev' (see line 1005)

Kirill also spotted that migrate_tasks() will have an instant NULL
deref because pick_next_task() will immediately deref prev.

Instead of fixing all the corner cases because migrate_tasks() can
pass in a NULL prev task in the unlikely case of hot-un-plug, provide
a fake task such that we can remove all the NULL checks from the far
more common paths.

A further problem; not previously spotted; is that because we pushed
pre_schedule() and idle_balance() into pick_next_task() we now need to
avoid those getting called and pulling more tasks on our dying CPU.

We avoid pull_{dl,rt}_task() by setting fake_task.prio to MAX_PRIO+1.
We also note that since we call pick_next_task() exactly the amount of
times we have runnable tasks present, we should never land in
idle_balance().

Fixes: 38033c37 ("sched: Push down pre_schedule() and idle_balance()")
Cc: Juri Lelli <juri.lelli@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Reported-by: NKirill Tkhai <tkhai@yandex.ru>
Reported-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20140212094930.GB3545@laptop.programming.kicks-ass.netSigned-off-by: NThomas Gleixner <tglx@linutronix.de>
      3f1d2a31
    • K
      sched/deadline: Remove useless dl_nr_total · 995b9ea4
      由 Kirill Tkhai 提交于 
      In deadline class we do not have group scheduling like in RT.

dl_nr_total is the same as dl_nr_running. So, one of them should
be removed.

Cc: Ingo Molnar <mingo@redhat.com>
Cc: Juri Lelli <juri.lelli@gmail.com>
Signed-off-by: NKirill Tkhai <tkhai@yandex.ru>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/368631392675853@web20h.yandex.ruSigned-off-by: NThomas Gleixner <tglx@linutronix.de>
      995b9ea4
    • J
      sched/deadline: Fix bad accounting of nr_running · 3d5f35bd
      由 Juri Lelli 提交于 
      Rostedt writes:

My test suite was locking up hard when enabling mmiotracer. This was due
to the mmiotracer placing all but one CPU offline. I found this out
when I was able to reproduce the bug with just my stress-cpu-hotplug
test. This bug baffled me because it would not always trigger, and
would only trigger on the first run after boot up. The
stress-cpu-hotplug test would crash hard the first run, or never crash
at all. But a new reboot may cause it to crash on the first run again.

I spent all week bisecting this, as I couldn't find a consistent
reproducer. I finally narrowed it down to the sched deadline patches,
and even more peculiar, to the commit that added the sched
deadline boot up self test to the latency tracer. Then it dawned on me
to what the bug was.

All it took was to run a task under sched deadline to screw up the CPU
hot plugging. This explained why it would lock up only on the first run
of the stress-cpu-hotplug test. The bug happened when the boot up self
test of the schedule latency tracer would test a deadline task. The
deadline task would corrupt something that would cause CPU hotplug to
fail. If it didn't corrupt it, the stress test would always work
(there's no other sched deadline tasks that would run to cause
problems). If it did corrupt on boot up, the first test would lockup
hard.

I proved this theory by running my deadline test program on another box,
and then run the stress-cpu-hotplug test, and it would now consistently
lock up. I could run stress-cpu-hotplug over and over with no problem,
but once I ran the deadline test, the next run of the
stress-cpu-hotplug would lock hard.

After adding lots of tracing to the code, I found the cause. The
function tracer showed that migrate_tasks() was stuck in an infinite
loop, where rq->nr_running never equaled 1 to break out of it. When I
added a trace_printk() to see what that number was, it was 335 and
never decrementing!

Looking at the deadline code I found:

static void __dequeue_task_dl(struct rq *rq, struct task_struct *p, int flags) {
	dequeue_dl_entity(&p->dl);
	dequeue_pushable_dl_task(rq, p);
}

static void dequeue_task_dl(struct rq *rq, struct task_struct *p, int flags) {
	update_curr_dl(rq);
	__dequeue_task_dl(rq, p, flags);

	dec_nr_running(rq);
}

And this:

	if (dl_runtime_exceeded(rq, dl_se)) {
		__dequeue_task_dl(rq, curr, 0);
		if (likely(start_dl_timer(dl_se, curr->dl.dl_boosted)))
			dl_se->dl_throttled = 1;
		else
			enqueue_task_dl(rq, curr, ENQUEUE_REPLENISH);

		if (!is_leftmost(curr, &rq->dl))
			resched_task(curr);
	}

Notice how we call __dequeue_task_dl() and in the else case we
call enqueue_task_dl()? Also notice that dequeue_task_dl() has
underscores where enqueue_task_dl() does not. The enqueue_task_dl()
calls inc_nr_running(rq), but __dequeue_task_dl() does not. This is
where we get nr_running out of sync.

[snip]

Another point where nr_running can get out of sync is when the dl_timer
fires:

	dl_se->dl_throttled = 0;
	if (p->on_rq) {
		enqueue_task_dl(rq, p, ENQUEUE_REPLENISH);
		if (task_has_dl_policy(rq->curr))
			check_preempt_curr_dl(rq, p, 0);
		else
			resched_task(rq->curr);

This patch does two things:

 - correctly accounts for throttled tasks (that are now considered
   !running);

 - fixes the bug, updating nr_running from {inc,dec}_dl_tasks(),
   since we risk to update it twice in some situations (e.g., a
   task is dequeued while it has exceeded its budget).

Cc: mingo@redhat.com
Cc: torvalds@linux-foundation.org
Cc: akpm@linux-foundation.org
Reported-by: NSteven Rostedt <rostedt@goodmis.org>
Reviewed-by: NSteven Rostedt <rostedt@goodmis.org>
Tested-by: NSteven Rostedt <rostedt@goodmis.org>
Signed-off-by: NJuri Lelli <juri.lelli@gmail.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1392884379-13744-1-git-send-email-juri.lelli@gmail.comSigned-off-by: NThomas Gleixner <tglx@linutronix.de>
      3d5f35bd
  29. 11 2月, 2014 1 次提交
    • P
      sched: Push down pre_schedule() and idle_balance() · 38033c37
      由 Peter Zijlstra 提交于 
      This patch both merged idle_balance() and pre_schedule() and pushes
both of them into pick_next_task().

Conceptually pre_schedule() and idle_balance() are rather similar,
both are used to pull more work onto the current CPU.

We cannot however first move idle_balance() into pre_schedule_fair()
since there is no guarantee the last runnable task is a fair task, and
thus we would miss newidle balances.

Similarly, the dl and rt pre_schedule calls must be ran before
idle_balance() since their respective tasks have higher priority and
it would not do to delay their execution searching for less important
tasks first.

However, by noticing that pick_next_tasks() already traverses the
sched_class hierarchy in the right order, we can get the right
behaviour and do away with both calls.

We must however change the special case optimization to also require
that prev is of sched_class_fair, otherwise we can miss doing a dl or
rt pull where we needed one.
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/n/tip-a8k6vvaebtn64nie345kx1je@git.kernel.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>
      38033c37
  31. 10 2月, 2014 1 次提交
  33. 09 2月, 2014 1 次提交
  35. 28 1月, 2014 1 次提交
  37. 16 1月, 2014 1 次提交
  39. 13 1月, 2014 5 次提交
    • P
      sched/deadline: Remove the sysctl_sched_dl knobs · 1724813d
      由 Peter Zijlstra 提交于 
      Remove the deadline specific sysctls for now. The problem with them is
that the interaction with the exisiting rt knobs is nearly impossible
to get right.

The current (as per before this patch) situation is that the rt and dl
bandwidth is completely separate and we enforce rt+dl < 100%. This is
undesirable because this means that the rt default of 95% leaves us
hardly any room, even though dl tasks are saver than rt tasks.

Another proposed solution was (a discarted patch) to have the dl
bandwidth be a fraction of the rt bandwidth. This is highly
confusing imo.

Furthermore neither proposal is consistent with the situation we
actually want; which is rt tasks ran from a dl server. In which case
the rt bandwidth is a direct subset of dl.

So whichever way we go, the introduction of dl controls at this point
is painful. Therefore remove them and instead share the rt budget.

This means that for now the rt knobs are used for dl admission control
and the dl runtime is accounted against the rt runtime. I realise that
this isn't entirely desirable either; but whatever we do we appear to
need to change the interface later, so better have a small interface
for now.
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-zpyqbqds1r0vyxtxza1e7rdc@git.kernel.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>
      1724813d
    • J
      sched/deadline: speed up SCHED_DEADLINE pushes with a push-heap · 6bfd6d72
      由 Juri Lelli 提交于 
      Data from tests confirmed that the original active load balancing
logic didn't scale neither in the number of CPU nor in the number of
tasks (as sched_rt does).

Here we provide a global data structure to keep track of deadlines
of the running tasks in the system. The structure is composed by
a bitmask showing the free CPUs and a max-heap, needed when the system
is heavily loaded.

The implementation and concurrent access scheme are kept simple by
design. However, our measurements show that we can compete with sched_rt
on large multi-CPUs machines [1].

Only the push path is addressed, the extension to use this structure
also for pull decisions is straightforward. However, we are currently
evaluating different (in order to decrease/avoid contention) data
structures to solve possibly both problems. We are also going to re-run
tests considering recent changes inside cpupri [2].

 [1] http://retis.sssup.it/~jlelli/papers/Ospert11Lelli.pdf
 [2] http://www.spinics.net/lists/linux-rt-users/msg06778.htmlSigned-off-by: NJuri Lelli <juri.lelli@gmail.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1383831828-15501-14-git-send-email-juri.lelli@gmail.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      6bfd6d72
    • D
      sched/deadline: Add bandwidth management for SCHED_DEADLINE tasks · 332ac17e
      由 Dario Faggioli 提交于 
      In order of deadline scheduling to be effective and useful, it is
important that some method of having the allocation of the available
CPU bandwidth to tasks and task groups under control.
This is usually called "admission control" and if it is not performed
at all, no guarantee can be given on the actual scheduling of the
-deadline tasks.

Since when RT-throttling has been introduced each task group have a
bandwidth associated to itself, calculated as a certain amount of
runtime over a period. Moreover, to make it possible to manipulate
such bandwidth, readable/writable controls have been added to both
procfs (for system wide settings) and cgroupfs (for per-group
settings).

Therefore, the same interface is being used for controlling the
bandwidth distrubution to -deadline tasks and task groups, i.e.,
new controls but with similar names, equivalent meaning and with
the same usage paradigm are added.

However, more discussion is needed in order to figure out how
we want to manage SCHED_DEADLINE bandwidth at the task group level.
Therefore, this patch adds a less sophisticated, but actually
very sensible, mechanism to ensure that a certain utilization
cap is not overcome per each root_domain (the single rq for !SMP
configurations).

Another main difference between deadline bandwidth management and
RT-throttling is that -deadline tasks have bandwidth on their own
(while -rt ones doesn't!), and thus we don't need an higher level
throttling mechanism to enforce the desired bandwidth.

This patch, therefore:

 - adds system wide deadline bandwidth management by means of:
    * /proc/sys/kernel/sched_dl_runtime_us,
    * /proc/sys/kernel/sched_dl_period_us,
   that determine (i.e., runtime / period) the total bandwidth
   available on each CPU of each root_domain for -deadline tasks;

 - couples the RT and deadline bandwidth management, i.e., enforces
   that the sum of how much bandwidth is being devoted to -rt
   -deadline tasks to stay below 100%.

This means that, for a root_domain comprising M CPUs, -deadline tasks
can be created until the sum of their bandwidths stay below:

    M * (sched_dl_runtime_us / sched_dl_period_us)

It is also possible to disable this bandwidth management logic, and
be thus free of oversubscribing the system up to any arbitrary level.
Signed-off-by: NDario Faggioli <raistlin@linux.it>
Signed-off-by: NJuri Lelli <juri.lelli@gmail.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1383831828-15501-12-git-send-email-juri.lelli@gmail.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      332ac17e
    • D
      sched/deadline: Add SCHED_DEADLINE inheritance logic · 2d3d891d
      由 Dario Faggioli 提交于 
      Some method to deal with rt-mutexes and make sched_dl interact with
the current PI-coded is needed, raising all but trivial issues, that
needs (according to us) to be solved with some restructuring of
the pi-code (i.e., going toward a proxy execution-ish implementation).

This is under development, in the meanwhile, as a temporary solution,
what this commits does is:

 - ensure a pi-lock owner with waiters is never throttled down. Instead,
   when it runs out of runtime, it immediately gets replenished and it's
   deadline is postponed;

 - the scheduling parameters (relative deadline and default runtime)
   used for that replenishments --during the whole period it holds the
   pi-lock-- are the ones of the waiting task with earliest deadline.

Acting this way, we provide some kind of boosting to the lock-owner,
still by using the existing (actually, slightly modified by the previous
commit) pi-architecture.

We would stress the fact that this is only a surely needed, all but
clean solution to the problem. In the end it's only a way to re-start
discussion within the community. So, as always, comments, ideas, rants,
etc.. are welcome! :-)
Signed-off-by: NDario Faggioli <raistlin@linux.it>
Signed-off-by: NJuri Lelli <juri.lelli@gmail.com>
[ Added !RT_MUTEXES build fix. ]
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1383831828-15501-11-git-send-email-juri.lelli@gmail.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      2d3d891d
    • H
      sched/deadline: Add period support for SCHED_DEADLINE tasks · 755378a4
      由 Harald Gustafsson 提交于 
      Make it possible to specify a period (different or equal than
deadline) for -deadline tasks. Relative deadlines (D_i) are used on
task arrivals to generate new scheduling (absolute) deadlines as "d =
t + D_i", and periods (P_i) to postpone the scheduling deadlines as "d
= d + P_i" when the budget is zero.

This is in general useful to model (and schedule) tasks that have slow
activation rates (long periods), but have to be scheduled soon once
activated (short deadlines).
Signed-off-by: NHarald Gustafsson <harald.gustafsson@ericsson.com>
Signed-off-by: NDario Faggioli <raistlin@linux.it>
Signed-off-by: NJuri Lelli <juri.lelli@gmail.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1383831828-15501-7-git-send-email-juri.lelli@gmail.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
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