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Date: Thu, 29 Oct 2020 10:51:51 -0000
From: "tip-bot2 for Peng Liu" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Peng Liu <iwtbavbm@...il.com>,
"Peter Zijlstra (Intel)" <peterz@...radead.org>,
Daniel Bristot de Oliveira <bristot@...hat.com>,
Juri Lelli <juri.lelli@...hat.com>, x86 <x86@...nel.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: [tip: sched/core] sched/deadline: Fix sched_dl_global_validate()
The following commit has been merged into the sched/core branch of tip:
Commit-ID: a57415f5d1e43c3a5c5d412cd85e2792d7ed9b11
Gitweb: https://git.kernel.org/tip/a57415f5d1e43c3a5c5d412cd85e2792d7ed9b11
Author: Peng Liu <iwtbavbm@...il.com>
AuthorDate: Thu, 08 Oct 2020 23:49:42 +08:00
Committer: Peter Zijlstra <peterz@...radead.org>
CommitterDate: Thu, 29 Oct 2020 11:00:29 +01:00
sched/deadline: Fix sched_dl_global_validate()
When change sched_rt_{runtime, period}_us, we validate that the new
settings should at least accommodate the currently allocated -dl
bandwidth:
sched_rt_handler()
--> sched_dl_bandwidth_validate()
{
new_bw = global_rt_runtime()/global_rt_period();
for_each_possible_cpu(cpu) {
dl_b = dl_bw_of(cpu);
if (new_bw < dl_b->total_bw) <-------
ret = -EBUSY;
}
}
But under CONFIG_SMP, dl_bw is per root domain , but not per CPU,
dl_b->total_bw is the allocated bandwidth of the whole root domain.
Instead, we should compare dl_b->total_bw against "cpus*new_bw",
where 'cpus' is the number of CPUs of the root domain.
Also, below annotation(in kernel/sched/sched.h) implied implementation
only appeared in SCHED_DEADLINE v2[1], then deadline scheduler kept
evolving till got merged(v9), but the annotation remains unchanged,
meaningless and misleading, update it.
* With respect to SMP, the bandwidth is given on a per-CPU basis,
* meaning that:
* - dl_bw (< 100%) is the bandwidth of the system (group) on each CPU;
* - dl_total_bw array contains, in the i-eth element, the currently
* allocated bandwidth on the i-eth CPU.
[1]: https://lore.kernel.org/lkml/1267385230.13676.101.camel@Palantir/
Fixes: 332ac17ef5bf ("sched/deadline: Add bandwidth management for SCHED_DEADLINE tasks")
Signed-off-by: Peng Liu <iwtbavbm@...il.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Daniel Bristot de Oliveira <bristot@...hat.com>
Acked-by: Juri Lelli <juri.lelli@...hat.com>
Link: https://lkml.kernel.org/r/db6bbda316048cda7a1bbc9571defde193a8d67e.1602171061.git.iwtbavbm@gmail.com
---
kernel/sched/deadline.c | 5 +++--
kernel/sched/sched.h | 42 +++++++++++++++++-----------------------
2 files changed, 21 insertions(+), 26 deletions(-)
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 98d96d4..0f75e95 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -2561,7 +2561,7 @@ int sched_dl_global_validate(void)
u64 new_bw = to_ratio(period, runtime);
u64 gen = ++dl_generation;
struct dl_bw *dl_b;
- int cpu, ret = 0;
+ int cpu, cpus, ret = 0;
unsigned long flags;
/*
@@ -2576,9 +2576,10 @@ int sched_dl_global_validate(void)
goto next;
dl_b = dl_bw_of(cpu);
+ cpus = dl_bw_cpus(cpu);
raw_spin_lock_irqsave(&dl_b->lock, flags);
- if (new_bw < dl_b->total_bw)
+ if (new_bw * cpus < dl_b->total_bw)
ret = -EBUSY;
raw_spin_unlock_irqrestore(&dl_b->lock, flags);
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 49a2dae..965b296 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -257,30 +257,6 @@ struct rt_bandwidth {
void __dl_clear_params(struct task_struct *p);
-/*
- * To keep the bandwidth of -deadline tasks and groups under control
- * we need some place where:
- * - store the maximum -deadline bandwidth of the system (the group);
- * - cache the fraction of that bandwidth that is currently allocated.
- *
- * This is all done in the data structure below. It is similar to the
- * one used for RT-throttling (rt_bandwidth), with the main difference
- * that, since here we are only interested in admission control, we
- * do not decrease any runtime while the group "executes", neither we
- * need a timer to replenish it.
- *
- * With respect to SMP, the bandwidth is given on a per-CPU basis,
- * meaning that:
- * - dl_bw (< 100%) is the bandwidth of the system (group) on each CPU;
- * - dl_total_bw array contains, in the i-eth element, the currently
- * allocated bandwidth on the i-eth CPU.
- * Moreover, groups consume bandwidth on each CPU, while tasks only
- * consume bandwidth on the CPU they're running on.
- * Finally, dl_total_bw_cpu is used to cache the index of dl_total_bw
- * that will be shown the next time the proc or cgroup controls will
- * be red. It on its turn can be changed by writing on its own
- * control.
- */
struct dl_bandwidth {
raw_spinlock_t dl_runtime_lock;
u64 dl_runtime;
@@ -292,6 +268,24 @@ static inline int dl_bandwidth_enabled(void)
return sysctl_sched_rt_runtime >= 0;
}
+/*
+ * To keep the bandwidth of -deadline tasks under control
+ * we need some place where:
+ * - store the maximum -deadline bandwidth of each cpu;
+ * - cache the fraction of bandwidth that is currently allocated in
+ * each root domain;
+ *
+ * This is all done in the data structure below. It is similar to the
+ * one used for RT-throttling (rt_bandwidth), with the main difference
+ * that, since here we are only interested in admission control, we
+ * do not decrease any runtime while the group "executes", neither we
+ * need a timer to replenish it.
+ *
+ * With respect to SMP, bandwidth is given on a per root domain basis,
+ * meaning that:
+ * - bw (< 100%) is the deadline bandwidth of each CPU;
+ * - total_bw is the currently allocated bandwidth in each root domain;
+ */
struct dl_bw {
raw_spinlock_t lock;
u64 bw;
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