| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-Id: <20230712133357.381137-3-pauld@redhat.com>
Date: Wed, 12 Jul 2023 09:33:57 -0400
From: Phil Auld <pauld@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: Juri Lelli <juri.lelli@...hat.com>, Ingo Molnar <mingo@...hat.com>,
Daniel Bristot de Oliveira <bristot@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Vincent Guittot <vincent.guittot@...aro.org>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Valentin Schneider <vschneid@...hat.com>,
Ben Segall <bsegall@...gle.com>,
Steven Rostedt <rostedt@...dmis.org>,
Mel Gorman <mgorman@...e.de>,
Frederic Weisbecker <frederic@...nel.org>,
Tejun Heo <tj@...nel.org>, Phil Auld <pauld@...hat.com>
Subject: [PATCH v6 2/2] Sched/fair: Block nohz tick_stop when cfs bandwidth in use
CFS bandwidth limits and NOHZ full don't play well together. Tasks
can easily run well past their quotas before a remote tick does
accounting. This leads to long, multi-period stalls before such
tasks can run again. Currently, when presented with these conflicting
requirements the scheduler is favoring nohz_full and letting the tick
be stopped. However, nohz tick stopping is already best-effort, there
are a number of conditions that can prevent it, whereas cfs runtime
bandwidth is expected to be enforced.
Make the scheduler favor bandwidth over stopping the tick by setting
TICK_DEP_BIT_SCHED when the only running task is a cfs task with
runtime limit enabled. We use cfs_b->hierarchical_quota to
determine if the task requires the tick.
Add check in pick_next_task_fair() as well since that is where
we have a handle on the task that is actually going to be running.
Add check in sched_can_stop_tick() to cover some edge cases such
as nr_running going from 2->1 and the 1 remains the running task.
Add sched_feat HZ_BW (off by default) to control the tick_stop
behavior.
Signed-off-by: Phil Auld <pauld@...hat.com>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Vincent Guittot <vincent.guittot@...aro.org>
Cc: Juri Lelli <juri.lelli@...hat.com>
Cc: Dietmar Eggemann <dietmar.eggemann@....com>
Cc: Valentin Schneider <vschneid@...hat.com>
Cc: Ben Segall <bsegall@...gle.com>
Cc: Frederic Weisbecker <frederic@...nel.org>
---
v6: restore check for fair_sched_class
v5: Reworked checks to use newly-fixed cfs_b->hierarchical_quota to
check for bw
constraints.
v4: Made checks for runtime_enabled hierarchical.
v3: Moved sched_cfs_bandwidth_active() prototype to sched.h outside of
guards to
silence -Wmissing-prototypes.
v2: Ben pointed out that the bit could get cleared in the dequeue path
if we migrate a newly enqueued task without preempting curr. Added a
check for that edge case to sched_can_stop_tick. Removed the call to
sched_can_stop_tick from sched_fair_update_stop_tick since it was
redundant.
kernel/sched/core.c | 26 ++++++++++++++++++++++
kernel/sched/fair.c | 49 +++++++++++++++++++++++++++++++++++++++++
kernel/sched/features.h | 2 ++
kernel/sched/sched.h | 1 +
4 files changed, 78 insertions(+)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index f80697a79baf..8a2ed4c0b709 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1194,6 +1194,20 @@ static void nohz_csd_func(void *info)
#endif /* CONFIG_NO_HZ_COMMON */
#ifdef CONFIG_NO_HZ_FULL
+static inline bool __need_bw_check(struct rq *rq, struct task_struct *p)
+{
+ if (rq->nr_running != 1)
+ return false;
+
+ if (p->sched_class != &fair_sched_class)
+ return false;
+
+ if (!task_on_rq_queued(p))
+ return false;
+
+ return true;
+}
+
bool sched_can_stop_tick(struct rq *rq)
{
int fifo_nr_running;
@@ -1229,6 +1243,18 @@ bool sched_can_stop_tick(struct rq *rq)
if (rq->nr_running > 1)
return false;
+ /*
+ * If there is one task and it has CFS runtime bandwidth constraints
+ * and it's on the cpu now we don't want to stop the tick.
+ * This check prevents clearing the bit if a newly enqueued task here is
+ * dequeued by migrating while the constrained task continues to run.
+ * E.g. going from 2->1 without going through pick_next_task().
+ */
+ if (sched_feat(HZ_BW) && __need_bw_check(rq, rq->curr)) {
+ if (cfs_task_bw_constrained(rq->curr))
+ return false;
+ }
+
return true;
}
#endif /* CONFIG_NO_HZ_FULL */
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index d9b3d4617e16..acd9f317aad1 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6140,6 +6140,46 @@ static void __maybe_unused unthrottle_offline_cfs_rqs(struct rq *rq)
rcu_read_unlock();
}
+bool cfs_task_bw_constrained(struct task_struct *p)
+{
+ struct cfs_rq *cfs_rq = task_cfs_rq(p);
+
+ if (!cfs_bandwidth_used())
+ return false;
+
+ if (cfs_rq->runtime_enabled ||
+ tg_cfs_bandwidth(cfs_rq->tg)->hierarchical_quota != RUNTIME_INF)
+ return true;
+
+ return false;
+}
+
+#ifdef CONFIG_NO_HZ_FULL
+/* called from pick_next_task_fair() */
+static void sched_fair_update_stop_tick(struct rq *rq, struct task_struct *p)
+{
+ int cpu = cpu_of(rq);
+
+ if (!sched_feat(HZ_BW) || !cfs_bandwidth_used())
+ return;
+
+ if (!tick_nohz_full_cpu(cpu))
+ return;
+
+ if (rq->nr_running != 1)
+ return;
+
+ /*
+ * We know there is only one task runnable and we've just picked it. The
+ * normal enqueue path will have cleared TICK_DEP_BIT_SCHED if we will
+ * be otherwise able to stop the tick. Just need to check if we are using
+ * bandwidth control.
+ */
+ if (cfs_task_bw_constrained(p))
+ tick_nohz_dep_set_cpu(cpu, TICK_DEP_BIT_SCHED);
+}
+#endif
+
#else /* CONFIG_CFS_BANDWIDTH */
static inline bool cfs_bandwidth_used(void)
@@ -6182,9 +6222,17 @@ static inline struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg)
static inline void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b) {}
static inline void update_runtime_enabled(struct rq *rq) {}
static inline void unthrottle_offline_cfs_rqs(struct rq *rq) {}
+bool cfs_task_bw_constrained(struct task_struct *p)
+{
+ return false;
+}
#endif /* CONFIG_CFS_BANDWIDTH */
+#if !defined(CONFIG_CFS_BANDWIDTH) || !defined(CONFIG_NO_HZ_FULL)
+static inline void sched_fair_update_stop_tick(struct rq *rq, struct task_struct *p) {}
+#endif
+
/**************************************************
* CFS operations on tasks:
*/
@@ -8098,6 +8146,7 @@ done: __maybe_unused;
hrtick_start_fair(rq, p);
update_misfit_status(p, rq);
+ sched_fair_update_stop_tick(rq, p);
return p;
diff --git a/kernel/sched/features.h b/kernel/sched/features.h
index ee7f23c76bd3..6fdf1fdf6b17 100644
--- a/kernel/sched/features.h
+++ b/kernel/sched/features.h
@@ -101,3 +101,5 @@ SCHED_FEAT(LATENCY_WARN, false)
SCHED_FEAT(ALT_PERIOD, true)
SCHED_FEAT(BASE_SLICE, true)
+
+SCHED_FEAT(HZ_BW, false)
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 63822c9238cc..d6d346bc78aa 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -465,6 +465,7 @@ extern void init_cfs_bandwidth(struct cfs_bandwidth *cfs_b, struct cfs_bandwidth
extern void __refill_cfs_bandwidth_runtime(struct cfs_bandwidth *cfs_b);
extern void start_cfs_bandwidth(struct cfs_bandwidth *cfs_b);
extern void unthrottle_cfs_rq(struct cfs_rq *cfs_rq);
+extern bool cfs_task_bw_constrained(struct task_struct *p);
extern void init_tg_rt_entry(struct task_group *tg, struct rt_rq *rt_rq,
struct sched_rt_entity *rt_se, int cpu,
--
2.31.1
Powered by blists - more mailing lists