Greetings,
I have two bug reports of absurd migration thread CPU usage, one of them
with a link to a bisection..
https://bugs.gentoo.org/show_bug.cgi?id=394487
..fingering d670ec13 - posix-cpu-timers: Cure SMP wobbles
I reproduced with my -rt kernel and 3.4, but didn't manage to reproduce
with the 3.0 NOPREEMPT kernel it was reported against.
Three options below, two tested in my -rt kernel.
A [ ] stop class doesn't do bean counting
B [ ] stop class counts beans like everybody else
C [ ] none of the above (not appended for brevity:)
I prefer B, elite class tasks eat beans.
A: sched: fix migration thread runtime bogosity
stop class threads don't do bean counting. Wipe the evidence of their
lowly birth, and don't try to use exec_start which is never updated.
vogelweide:/:[0]# ps l 824
F UID PID PPID PRI NI VSZ RSS WCHAN STAT TTY TIME COMMAND
1 0 824 2 -100 - 0 0 cpu_st S ? 2799:06
[migration/57]
Signed-off-by: Mike Galbraith <[email protected]>
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 82ad284..82a78a6 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -974,6 +974,13 @@ void sched_set_stop_task(int cpu, struct task_struct *stop)
sched_setscheduler_nocheck(stop, SCHED_FIFO, ¶m);
stop->sched_class = &stop_sched_class;
+
+ /* Zero stale values for our non-accountable thread. */
+ stop->se.exec_start = 0;
+ stop->se.sum_exec_runtime = 0;
+ stop->se.prev_sum_exec_runtime = 0;
+ stop->stime = stop->stimescaled = 0;
+ stop->nvcsw = stop->nivcsw = 0;
}
cpu_rq(cpu)->stop = stop;
@@ -2803,7 +2810,8 @@ unsigned long long task_sched_runtime(struct task_struct
*p)
u64 ns = 0;
rq = task_rq_lock(p, &flags);
- ns = p->se.sum_exec_runtime + do_task_delta_exec(p, rq);
+ if (likely(p != rq->stop)
+ ns = p->se.sum_exec_runtime + do_task_delta_exec(p, rq);
task_rq_unlock(rq, p, &flags);
return ns;
B: sched: fix migration thread runtime bogosity
stop class threads need to do bean counting lest the below happen.
vogelweide:/:[0]# ps l 824
F UID PID PPID PRI NI VSZ RSS WCHAN STAT TTY TIME COMMAND
1 0 824 2 -100 - 0 0 cpu_st S ? 2799:06
[migration/57]
Signed-off-by: Mike Galbraith <[email protected]>
diff --git a/kernel/sched/stop_task.c b/kernel/sched/stop_task.c
index 7b386e8..da5eb5b 100644
--- a/kernel/sched/stop_task.c
+++ b/kernel/sched/stop_task.c
@@ -27,8 +27,10 @@ static struct task_struct *pick_next_task_stop(struct rq *rq)
{
struct task_struct *stop = rq->stop;
- if (stop && stop->on_rq)
+ if (stop && stop->on_rq) {
+ stop->se.exec_start = rq->clock_task;
return stop;
+ }
return NULL;
}
@@ -52,6 +54,21 @@ static void yield_task_stop(struct rq *rq)
static void put_prev_task_stop(struct rq *rq, struct task_struct *prev)
{
+ struct task_struct *curr = rq->curr;
+ u64 delta_exec;
+
+ delta_exec = rq->clock_task - curr->se.exec_start;
+ if (unlikely((s64)delta_exec < 0))
+ delta_exec = 0;
+
+ schedstat_set(curr->se.statistics.exec_max,
+ max(curr->se.statistics.exec_max, delta_exec));
+
+ curr->se.sum_exec_runtime += delta_exec;
+ account_group_exec_runtime(curr, delta_exec);
+
+ curr->se.exec_start = rq->clock_task;
+ cpuacct_charge(curr, delta_exec);
}
static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued)
@@ -60,6 +77,9 @@ static void task_tick_stop(struct rq *rq, struct task_struct
*curr, int queued)
static void set_curr_task_stop(struct rq *rq)
{
+ struct task_struct *stop = rq->stop;
+
+ stop->se.exec_start = rq->clock_task;
}
static void switched_to_stop(struct rq *rq, struct task_struct *p)
--
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