linux-stable.git/kernel/sched/deadline.c, branch linux-3.18.y

sched/deadline: Use deadline instead of period when calculating overflow

2017-12-20T09:01:30+00:00

[ Upstream commit 2317d5f1c34913bac5971d93d69fb6c31bb74670 ]

I was testing Daniel's changes with his test case, and tweaked it a
little. Instead of having the runtime equal to the deadline, I
increased the deadline ten fold.

Daniel's test case had:

	attr.sched_runtime  = 2 * 1000 * 1000;		/* 2 ms */
	attr.sched_deadline = 2 * 1000 * 1000;		/* 2 ms */
	attr.sched_period   = 2 * 1000 * 1000 * 1000;	/* 2 s */

To make it more interesting, I changed it to:

	attr.sched_runtime  =  2 * 1000 * 1000;		/* 2 ms */
	attr.sched_deadline = 20 * 1000 * 1000;		/* 20 ms */
	attr.sched_period   =  2 * 1000 * 1000 * 1000;	/* 2 s */

The results were rather surprising. The behavior that Daniel's patch
was fixing came back. The task started using much more than .1% of the
CPU. More like 20%.

Looking into this I found that it was due to the dl_entity_overflow()
constantly returning true. That's because it uses the relative period
against relative runtime vs the absolute deadline against absolute
runtime.

  runtime / (deadline - t) > dl_runtime / dl_period

There's even a comment mentioning this, and saying that when relative
deadline equals relative period, that the equation is the same as using
deadline instead of period. That comment is backwards! What we really
want is:

  runtime / (deadline - t) > dl_runtime / dl_deadline

We care about if the runtime can make its deadline, not its period. And
then we can say "when the deadline equals the period, the equation is
the same as using dl_period instead of dl_deadline".

After correcting this, now when the task gets enqueued, it can throttle
correctly, and Daniel's fix to the throttling of sleeping deadline
tasks works even when the runtime and deadline are not the same.

Signed-off-by: Steven Rostedt (VMware) 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Daniel Bristot de Oliveira 
Cc: Juri Lelli 
Cc: Linus Torvalds 
Cc: Luca Abeni 
Cc: Mike Galbraith 
Cc: Peter Zijlstra 
Cc: Romulo Silva de Oliveira 
Cc: Steven Rostedt 
Cc: Thomas Gleixner 
Cc: Tommaso Cucinotta 
Link: http://lkml.kernel.org/r/02135a27f1ae3fe5fd032568a5a2f370e190e8d7.1488392936.git.bristot@redhat.com
Signed-off-by: Ingo Molnar 
Signed-off-by: Sasha Levin 
Signed-off-by: Greg Kroah-Hartman

sched/deadline: Avoid double-accounting in case of missed deadlines

2015-01-16T14:59:54+00:00

commit 269ad8015a6b2bb1cf9e684da4921eb6fa0a0c88 upstream.

The dl_runtime_exceeded() function is supposed to ckeck if
a SCHED_DEADLINE task must be throttled, by checking if its
current runtime is <= 0. However, it also checks if the
scheduling deadline has been missed (the current time is
larger than the current scheduling deadline), further
decreasing the runtime if this happens.
This "double accounting" is wrong:

- In case of partitioned scheduling (or single CPU), this
  happens if task_tick_dl() has been called later than expected
  (due to small HZ values). In this case, the current runtime is
  also negative, and replenish_dl_entity() can take care of the
  deadline miss by recharging the current runtime to a value smaller
  than dl_runtime

- In case of global scheduling on multiple CPUs, scheduling
  deadlines can be missed even if the task did not consume more
  runtime than expected, hence penalizing the task is wrong

This patch fix this problem by throttling a SCHED_DEADLINE task
only when its runtime becomes negative, and not modifying the runtime

Signed-off-by: Luca Abeni 
Signed-off-by: Peter Zijlstra (Intel) 
Acked-by: Juri Lelli 
Cc: Dario Faggioli 
Cc: Linus Torvalds 
Link: http://lkml.kernel.org/r/1418813432-20797-3-git-send-email-luca.abeni@unitn.it
Signed-off-by: Ingo Molnar 
Signed-off-by: Greg Kroah-Hartman

sched/deadline: Fix migration of SCHED_DEADLINE tasks

2015-01-16T14:59:54+00:00

commit 6a503c3be937d275113b702e0421e5b0720abe8a upstream.

According to global EDF, tasks should be migrated between runqueues
without checking if their scheduling deadlines and runtimes are valid.
However, SCHED_DEADLINE currently performs such a check:
a migration happens doing:

	deactivate_task(rq, next_task, 0);
	set_task_cpu(next_task, later_rq->cpu);
	activate_task(later_rq, next_task, 0);

which ends up calling dequeue_task_dl(), setting the new CPU, and then
calling enqueue_task_dl().

enqueue_task_dl() then calls enqueue_dl_entity(), which calls
update_dl_entity(), which can modify scheduling deadline and runtime,
breaking global EDF scheduling.

As a result, some of the properties of global EDF are not respected:
for example, a taskset {(30, 80), (40, 80), (120, 170)} scheduled on
two cores can have unbounded response times for the third task even
if 30/80+40/80+120/170 = 1.5809 < 2

This can be fixed by invoking update_dl_entity() only in case of
wakeup, or if this is a new SCHED_DEADLINE task.

Signed-off-by: Luca Abeni 
Signed-off-by: Peter Zijlstra (Intel) 
Acked-by: Juri Lelli 
Cc: Dario Faggioli 
Cc: Linus Torvalds 
Link: http://lkml.kernel.org/r/1418813432-20797-2-git-send-email-luca.abeni@unitn.it
Signed-off-by: Ingo Molnar 
Signed-off-by: Greg Kroah-Hartman

sched/cputime: Fix clock_nanosleep()/clock_gettime() inconsistency

2014-11-16T09:04:20+00:00

Commit d670ec13178d0 "posix-cpu-timers: Cure SMP wobbles" fixes one glibc
test case in cost of breaking another one. After that commit, calling
clock_nanosleep(TIMER_ABSTIME, X) and then clock_gettime(&Y) can result
of Y time being smaller than X time.

Reproducer/tester can be found further below, it can be compiled and ran by:

	gcc -o tst-cpuclock2 tst-cpuclock2.c -pthread
	while ./tst-cpuclock2 ; do : ; done

This reproducer, when running on a buggy kernel, will complain
about "clock_gettime difference too small".

Issue happens because on start in thread_group_cputimer() we initialize
sum_exec_runtime of cputimer with threads runtime not yet accounted and
then add the threads runtime to running cputimer again on scheduler
tick, making it's sum_exec_runtime bigger than actual threads runtime.

KOSAKI Motohiro posted a fix for this problem, but that patch was never
applied: https://lkml.org/lkml/2013/5/26/191 .

This patch takes different approach to cure the problem. It calls
update_curr() when cputimer starts, that assure we will have updated
stats of running threads and on the next schedule tick we will account
only the runtime that elapsed from cputimer start. That also assure we
have consistent state between cpu times of individual threads and cpu
time of the process consisted by those threads.

Full reproducer (tst-cpuclock2.c):

	#define _GNU_SOURCE
	#include 
	#include 
	#include 
	#include 
	#include 
	#include 
	#include 

	/* Parameters for the Linux kernel ABI for CPU clocks.  */
	#define CPUCLOCK_SCHED          2
	#define MAKE_PROCESS_CPUCLOCK(pid, clock) \
		((~(clockid_t) (pid) << 3) | (clockid_t) (clock))

	static pthread_barrier_t barrier;

	/* Help advance the clock.  */
	static void *chew_cpu(void *arg)
	{
		pthread_barrier_wait(&barrier);
		while (1) ;

		return NULL;
	}

	/* Don't use the glibc wrapper.  */
	static int do_nanosleep(int flags, const struct timespec *req)
	{
		clockid_t clock_id = MAKE_PROCESS_CPUCLOCK(0, CPUCLOCK_SCHED);

		return syscall(SYS_clock_nanosleep, clock_id, flags, req, NULL);
	}

	static int64_t tsdiff(const struct timespec *before, const struct timespec *after)
	{
		int64_t before_i = before->tv_sec * 1000000000ULL + before->tv_nsec;
		int64_t after_i = after->tv_sec * 1000000000ULL + after->tv_nsec;

		return after_i - before_i;
	}

	int main(void)
	{
		int result = 0;
		pthread_t th;

		pthread_barrier_init(&barrier, NULL, 2);

		if (pthread_create(&th, NULL, chew_cpu, NULL) != 0) {
			perror("pthread_create");
			return 1;
		}

		pthread_barrier_wait(&barrier);

		/* The test.  */
		struct timespec before, after, sleeptimeabs;
		int64_t sleepdiff, diffabs;
		const struct timespec sleeptime = {.tv_sec = 0,.tv_nsec = 100000000 };

		/* The relative nanosleep.  Not sure why this is needed, but its presence
		   seems to make it easier to reproduce the problem.  */
		if (do_nanosleep(0, &sleeptime) != 0) {
			perror("clock_nanosleep");
			return 1;
		}

		/* Get the current time.  */
		if (clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &before) < 0) {
			perror("clock_gettime[2]");
			return 1;
		}

		/* Compute the absolute sleep time based on the current time.  */
		uint64_t nsec = before.tv_nsec + sleeptime.tv_nsec;
		sleeptimeabs.tv_sec = before.tv_sec + nsec / 1000000000;
		sleeptimeabs.tv_nsec = nsec % 1000000000;

		/* Sleep for the computed time.  */
		if (do_nanosleep(TIMER_ABSTIME, &sleeptimeabs) != 0) {
			perror("absolute clock_nanosleep");
			return 1;
		}

		/* Get the time after the sleep.  */
		if (clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &after) < 0) {
			perror("clock_gettime[3]");
			return 1;
		}

		/* The time after sleep should always be equal to or after the absolute sleep
		   time passed to clock_nanosleep.  */
		sleepdiff = tsdiff(&sleeptimeabs, &after);
		if (sleepdiff < 0) {
			printf("absolute clock_nanosleep woke too early: %" PRId64 "\n", sleepdiff);
			result = 1;

			printf("Before %llu.%09llu\n", before.tv_sec, before.tv_nsec);
			printf("After  %llu.%09llu\n", after.tv_sec, after.tv_nsec);
			printf("Sleep  %llu.%09llu\n", sleeptimeabs.tv_sec, sleeptimeabs.tv_nsec);
		}

		/* The difference between the timestamps taken before and after the
		   clock_nanosleep call should be equal to or more than the duration of the
		   sleep.  */
		diffabs = tsdiff(&before, &after);
		if (diffabs < sleeptime.tv_nsec) {
			printf("clock_gettime difference too small: %" PRId64 "\n", diffabs);
			result = 1;
		}

		pthread_cancel(th);

		return result;
	}

Signed-off-by: Stanislaw Gruszka 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: Rik van Riel 
Cc: Frederic Weisbecker 
Cc: KOSAKI Motohiro 
Cc: Oleg Nesterov 
Cc: Linus Torvalds 
Link: http://lkml.kernel.org/r/20141112155843.GA24803@redhat.com
Signed-off-by: Ingo Molnar

sched/dl: Fix preemption checks

2014-10-28T09:46:10+00:00

1) switched_to_dl() check is wrong. We reschedule only
   if rq->curr is deadline task, and we do not reschedule
   if it's a lower priority task. But we must always
   preempt a task of other classes.

2) dl_task_timer():
   Policy does not change in case of priority inheritance.
   rt_mutex_setprio() changes prio, while policy remains old.

So we lose some balancing logic in dl_task_timer() and
switched_to_dl() when we check policy instead of priority. Boosted
task may be rq->curr.

(I didn't change switched_from_dl() because no check is necessary
there at all).

I've looked at this place(switched_to_dl) several times and even fixed
this function, but found just now...  I suppose some performance tests
may work better after this.

Signed-off-by: Kirill Tkhai 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: Juri Lelli 
Cc: Linus Torvalds 
Link: http://lkml.kernel.org/r/1413909356.19914.128.camel@tkhai
Signed-off-by: Ingo Molnar

sched/deadline: Fix races between rt_mutex_setprio() and dl_task_timer()

2014-10-28T09:46:01+00:00

dl_task_timer() is racy against several paths. Daniel noticed that
the replenishment timer may experience a race condition against an
enqueue_dl_entity() called from rt_mutex_setprio(). With his own
words:

 rt_mutex_setprio() resets p->dl.dl_throttled. So the pattern is:
 start_dl_timer() throttled = 1, rt_mutex_setprio() throlled = 0,
 sched_switch() -> enqueue_task(), dl_task_timer-> enqueue_task()
 throttled is 0

=> BUG_ON(on_dl_rq(dl_se)) fires as the scheduling entity is already
enqueued on the -deadline runqueue.

As we do for the other races, we just bail out in the replenishment
timer code.

Reported-by: Daniel Wagner 
Tested-by: Daniel Wagner 
Signed-off-by: Juri Lelli 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: vincent@legout.info
Cc: Dario Faggioli 
Cc: Michael Trimarchi 
Cc: Fabio Checconi 
Cc: Linus Torvalds 
Link: http://lkml.kernel.org/r/1414142198-18552-5-git-send-email-juri.lelli@arm.com
Signed-off-by: Ingo Molnar

sched/deadline: Don't replenish from a !SCHED_DEADLINE entity

2014-10-28T09:46:00+00:00

In the deboost path, right after the dl_boosted flag has been
reset, we can currently end up replenishing using -deadline
parameters of a !SCHED_DEADLINE entity. This of course causes
a bug, as those parameters are empty.

In the case depicted above it is safe to simply bail out, as
the deboosted task is going to be back to its original scheduling
class anyway.

Reported-by: Daniel Wagner 
Tested-by: Daniel Wagner 
Signed-off-by: Juri Lelli 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: Linus Torvalds 
Cc: vincent@legout.info
Cc: Dario Faggioli 
Cc: Michael Trimarchi 
Cc: Fabio Checconi 
Link: http://lkml.kernel.org/r/1414142198-18552-4-git-send-email-juri.lelli@arm.com
Signed-off-by: Ingo Molnar

Merge branch 'for-3.18-consistent-ops' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/percpu

2014-10-15T05:48:18+00:00

Pull percpu consistent-ops changes from Tejun Heo:
"Way back, before the current percpu allocator was implemented, static
and dynamic percpu memory areas were allocated and handled separately
and had their own accessors. The distinction has been gone for many
years now; however, the now duplicate two sets of accessors remained
with the pointer based ones - this_cpu_*() - evolving various other
operations over time. During the process, we also accumulated other
inconsistent operations.

This pull request contains Christoph's patches to clean up the
duplicate accessor situation. __get_cpu_var() uses are replaced with
with this_cpu_ptr() and __this_cpu_ptr() with raw_cpu_ptr().

Unfortunately, the former sometimes is tricky thanks to C being a bit
messy with the distinction between lvalues and pointers, which led to
a rather ugly solution for cpumask_var_t involving the introduction of
this_cpu_cpumask_var_ptr().

This converts most of the uses but not all. Christoph will follow up
with the remaining conversions in this merge window and hopefully
remove the obsolete accessors"

* 'for-3.18-consistent-ops' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/percpu: (38 commits)
irqchip: Properly fetch the per cpu offset
percpu: Resolve ambiguities in __get_cpu_var/cpumask_var_t -fix
ia64: sn_nodepda cannot be assigned to after this_cpu conversion. Use __this_cpu_write.
percpu: Resolve ambiguities in __get_cpu_var/cpumask_var_t
Revert "powerpc: Replace __get_cpu_var uses"
percpu: Remove __this_cpu_ptr
clocksource: Replace __this_cpu_ptr with raw_cpu_ptr
sparc: Replace __get_cpu_var uses
avr32: Replace __get_cpu_var with __this_cpu_write
blackfin: Replace __get_cpu_var uses
tile: Use this_cpu_ptr() for hardware counters
tile: Replace __get_cpu_var uses
powerpc: Replace __get_cpu_var uses
alpha: Replace __get_cpu_var
ia64: Replace __get_cpu_var uses
s390: cio driver &__get_cpu_var replacements
s390: Replace __get_cpu_var uses
mips: Replace __get_cpu_var uses
MIPS: Replace __get_cpu_var uses in FPU emulator.
arm: Replace __this_cpu_ptr with raw_cpu_ptr
...

sched/deadline: Fix inter- exclusive cpusets migrations

2014-09-24T12:46:57+00:00

Users can perform clustered scheduling using the cpuset facility.
After an exclusive cpuset is created, task migrations happen only
between CPUs belonging to the same cpuset. Inter- cpuset migrations
can only happen when the user requires so, moving a task between
different cpusets. This behaviour is broken in SCHED_DEADLINE, as
currently spurious inter- cpuset migration may happen without user
intervention.

This patch fix the problem (and shuffles the code a bit to improve
clarity).

Signed-off-by: Juri Lelli 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: raistlin@linux.it
Cc: michael@amarulasolutions.com
Cc: fchecconi@gmail.com
Cc: daniel.wagner@bmw-carit.de
Cc: vincent@legout.info
Cc: luca.abeni@unitn.it
Cc: Linus Torvalds 
Link: http://lkml.kernel.org/r/1411118561-26323-4-git-send-email-juri.lelli@arm.com
Signed-off-by: Ingo Molnar

sched/deadline: Clear dl_entity params when setscheduling to different class

2014-09-24T12:46:56+00:00

When a task is using SCHED_DEADLINE and the user setschedules it to a
different class its sched_dl_entity static parameters are not cleaned
up. This causes a bug if the user sets it back to SCHED_DEADLINE with
the same parameters again.  The problem resides in the check we
perform at the very beginning of dl_overflow():

	if (new_bw == p->dl.dl_bw)
		return 0;

This condition is met in the case depicted above, so the function
returns and dl_b->total_bw is not updated (the p->dl.dl_bw is not
added to it). After this, admission control is broken.

This patch fixes the thing, properly clearing static parameters for a
task that ceases to use SCHED_DEADLINE.

Reported-by: Daniele Alessandrelli 
Reported-by: Daniel Wagner 
Reported-by: Vincent Legout 
Tested-by: Luca Abeni 
Tested-by: Daniel Wagner 
Tested-by: Vincent Legout 
Signed-off-by: Juri Lelli 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: Fabio Checconi 
Cc: Dario Faggioli 
Cc: Michael Trimarchi 
Cc: Linus Torvalds 
Link: http://lkml.kernel.org/r/1411118561-26323-2-git-send-email-juri.lelli@arm.com
Signed-off-by: Ingo Molnar