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authorLuca Abeni <luca.abeni@santannapisa.it>2017-05-18 22:13:32 +0200
committerIngo Molnar <mingo@kernel.org>2017-06-08 10:31:51 +0200
commit4da3abcefe178c650033f371e94fa10e80bce167 (patch)
tree12d6b708fa1911e1053f85a0b29aab5bd41767f2 /kernel/sched
parentc52f14d384628db0217a7a9080ab800d5ffb2d72 (diff)
sched/deadline: Do not reclaim the whole CPU bandwidth
Original GRUB tends to reclaim 100% of the CPU time... And this allows a CPU hog to starve non-deadline tasks. To address this issue, allow the scheduler to reclaim only a specified fraction of CPU time, stored in the new "bw_ratio" field of the dl runqueue structure. Tested-by: Daniel Bristot de Oliveira <bristot@redhat.com> Signed-off-by: Luca Abeni <luca.abeni@santannapisa.it> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Claudio Scordino <claudio@evidence.eu.com> Cc: Joel Fernandes <joelaf@google.com> Cc: Juri Lelli <juri.lelli@arm.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mathieu Poirier <mathieu.poirier@linaro.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Tommaso Cucinotta <tommaso.cucinotta@sssup.it> Link: http://lkml.kernel.org/r/1495138417-6203-6-git-send-email-luca.abeni@santannapisa.it Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/sched')
-rw-r--r--kernel/sched/core.c11
-rw-r--r--kernel/sched/deadline.c12
-rw-r--r--kernel/sched/sched.h8
3 files changed, 30 insertions, 1 deletions
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index b68a1fa05244..7abd06400a98 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6759,6 +6759,16 @@ static int sched_dl_global_validate(void)
return ret;
}
+void init_dl_rq_bw_ratio(struct dl_rq *dl_rq)
+{
+ if (global_rt_runtime() == RUNTIME_INF) {
+ dl_rq->bw_ratio = 1 << RATIO_SHIFT;
+ } else {
+ dl_rq->bw_ratio = to_ratio(global_rt_runtime(),
+ global_rt_period()) >> (BW_SHIFT - RATIO_SHIFT);
+ }
+}
+
static void sched_dl_do_global(void)
{
u64 new_bw = -1;
@@ -6784,6 +6794,7 @@ static void sched_dl_do_global(void)
raw_spin_unlock_irqrestore(&dl_b->lock, flags);
rcu_read_unlock_sched();
+ init_dl_rq_bw_ratio(&cpu_rq(cpu)->dl);
}
}
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 0bee537554f6..6a0614b9c8d7 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -268,6 +268,7 @@ void init_dl_rq(struct dl_rq *dl_rq)
#endif
dl_rq->running_bw = 0;
+ init_dl_rq_bw_ratio(dl_rq);
}
#ifdef CONFIG_SMP
@@ -924,11 +925,20 @@ extern bool sched_rt_bandwidth_account(struct rt_rq *rt_rq);
* Uact is the (per-runqueue) active utilization.
* Since rq->dl.running_bw contains Uact * 2^BW_SHIFT, the result
* has to be shifted right by BW_SHIFT.
+ * To reclaim only a fraction Umax of the CPU time, the
+ * runtime accounting rule is modified as
+ * "dq = -Uact / Umax dt"; since rq->dl.bw_ratio contains
+ * 2^RATIO_SHIFT / Umax, delta is multiplied by bw_ratio and shifted
+ * right by RATIO_SHIFT.
+ * Since delta is a 64 bit variable, to have an overflow its value
+ * should be larger than 2^(64 - 20 - 8), which is more than 64 seconds.
+ * So, overflow is not an issue here.
*/
u64 grub_reclaim(u64 delta, struct rq *rq)
{
delta *= rq->dl.running_bw;
- delta >>= BW_SHIFT;
+ delta *= rq->dl.bw_ratio;
+ delta >>= BW_SHIFT + RATIO_SHIFT;
return delta;
}
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index bb409ef40120..878fe757d6ad 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -565,6 +565,12 @@ struct dl_rq {
* task blocks
*/
u64 running_bw;
+
+ /*
+ * Inverse of the fraction of CPU utilization that can be reclaimed
+ * by the GRUB algorithm.
+ */
+ u64 bw_ratio;
};
#ifdef CONFIG_SMP
@@ -1495,9 +1501,11 @@ extern struct dl_bandwidth def_dl_bandwidth;
extern void init_dl_bandwidth(struct dl_bandwidth *dl_b, u64 period, u64 runtime);
extern void init_dl_task_timer(struct sched_dl_entity *dl_se);
extern void init_dl_inactive_task_timer(struct sched_dl_entity *dl_se);
+extern void init_dl_rq_bw_ratio(struct dl_rq *dl_rq);
#define BW_SHIFT 20
#define BW_UNIT (1 << BW_SHIFT)
+#define RATIO_SHIFT 8
unsigned long to_ratio(u64 period, u64 runtime);
extern void init_entity_runnable_average(struct sched_entity *se);