| 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: <20220512163534.2572-6-vincent.guittot@linaro.org>
Date: Thu, 12 May 2022 18:35:32 +0200
From: Vincent Guittot <vincent.guittot@...aro.org>
To: mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com,
linux-kernel@...r.kernel.org, parth@...ux.ibm.com
Cc: qais.yousef@....com, chris.hyser@...cle.com,
valentin.schneider@....com, patrick.bellasi@...bug.net,
David.Laight@...lab.com, pjt@...gle.com, pavel@....cz,
tj@...nel.org, qperret@...gle.com, tim.c.chen@...ux.intel.com,
joshdon@...gle.com, Vincent Guittot <vincent.guittot@...aro.org>
Subject: [PATCH v2 5/7] sched/fair: Take into account latency nice at wakeup
Take into account the nice latency priority of a thread when deciding to
preempt the current running thread. We don't want to provide more CPU
bandwidth to a thread but reorder the scheduling to run latency sensitive
task first whenever possible.
As long as a thread didn't use its bandwidth, it will be able to preempt
the current thread.
At the opposite, a thread with a low latency priority will preempt current
thread at wakeup only to keep fair CPU bandwidth sharing. Otherwise it will
wait for the tick to get its sched slice.
curr vruntime
|
sysctl_sched_wakeup_granularity
<-->
----------------------------------|----|-----------------------|---------------
| |<--------------------->
| . sysctl_sched_latency
| .
default/current latency entity | .
| .
1111111111111111111111111111111111|0000|-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-
se preempts curr at wakeup ------>|<- se doesn't preempt curr -----------------
| .
| .
| .
low latency entity | .
---------------------->|
% of sysctl_sched_latency |
1111111111111111111111111111111111111111111111111111111111|0000|-1-1-1-1-1-1-1-
preempt ------------------------------------------------->|<- do not preempt --
| .
| .
| .
high latency entity | .
|<-----------------------| .
| % of sysctl_sched_latency .
111111111|0000|-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1
preempt->|<- se doesn't preempt curr ------------------------------------------
Tests results of nice latency impact on heavy load like hackbench:
hackbench -l (2560 / group) -g group
group latency 0 latency 19
1 1.399(+/- 1.27%) 1.357(+/- 1.48%) + 3%
4 1.422(+/- 4.69%) 1.267(+/- 2.39%) +11%
8 1.334(+/- 2.92%) 1.290(+/- 0.92%) + 3%
16 1.353(+/- 1.37%) 1.310(+/- 0.35%) + 3%
hackbench -p -l (2560 / group) -g group
group
1 1.450(+/- 9.14%) 0.853(+/- 3.23%) +41%
4 1.539(+/- 6.41%) 0.754(+/- 3.96%) +51%
8 1.380(+/- 8.04%) 0.687(+/- 5.30%) +50%
16 0.774(+/- 6.30%) 0.688(+/- 3.11%) +11%
By deacreasing the latency prio, we reduce the number of preemption at
wakeup and help hackbench making progress.
Test results of nice latency impact on short live load like cyclictest
while competing with heavy load like hackbench:
hackbench -l 10000 -g group &
cyclictest --policy other -D 5 -q -n
latency 0 latency -20
group min avg max min avg max
0 15 18 28 17 17 27
1 65 386 9154 62 92 6268
4 63 447 14623 54 93 7655
8 63 847 43705 49 124 26500
16 53 1081 66523 44 199 30185
group = 0 means that hackbench is not running.
The avg is significantly improved with nice latency -20 especially with
large number of groups but min and max remain quite similar. If we add the
histogram parameters to get details of latency, we have :
hackbench -l 10000 -g 16 &
cyclictest --policy other -D 5 -q -n -H 20000 --histfile data.txt
latency 0 latency -20
Min Latencies: 63 62
Avg Latencies: 1129 132
Max Latencies: 71331 16762
50% latencies: 92 85
75% latencies: 622 90
85% latencies: 1038 93
90% latencies: 1371 96
95% latencies: 5304 100
99% latencies: 17329 137
With percentile details, we see the benefit of nice latency -20 as
1% of the latencies stays above 137us whereas the default latency has
got 25% are above 322us and 15% over the 1ms.
Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
---
For v1, it has been discussed the opportunity to take into account latency_prio
in other places than check_preempt_wakeup().
The fast wakeup path is mainly about quickly looking for an idle CPU and I
don't see any place where the added complexity would provide obvious benefit.
The only place could be wake_affine_weight when we already compare the load;
here we could also check latency_nice prio of current tasks.
The slow path is mainly/only used for exec and fork and I wonder if there is
cases where we would like a newly forked task to preempt current one as soon
as possible as an example.
So I haven't add any new place that takes into account latency_prio for now.
include/linux/sched.h | 4 ++-
init/init_task.c | 2 +-
kernel/sched/core.c | 34 +++++++++++++++++----
kernel/sched/debug.c | 2 +-
kernel/sched/fair.c | 69 +++++++++++++++++++++++++++++++++++++++++--
kernel/sched/sched.h | 12 ++++++++
6 files changed, 112 insertions(+), 11 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 34c6c9c2797c..d991cbd972ea 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -560,6 +560,8 @@ struct sched_entity {
unsigned long runnable_weight;
#endif
+ int latency_weight;
+
#ifdef CONFIG_SMP
/*
* Per entity load average tracking.
@@ -775,7 +777,7 @@ struct task_struct {
int static_prio;
int normal_prio;
unsigned int rt_priority;
- int latency_nice;
+ int latency_prio;
struct sched_entity se;
struct sched_rt_entity rt;
diff --git a/init/init_task.c b/init/init_task.c
index 225d11a39bc9..e98c71f24981 100644
--- a/init/init_task.c
+++ b/init/init_task.c
@@ -78,7 +78,7 @@ struct task_struct init_task
.prio = MAX_PRIO - 20,
.static_prio = MAX_PRIO - 20,
.normal_prio = MAX_PRIO - 20,
- .latency_nice = DEFAULT_LATENCY_NICE,
+ .latency_prio = NICE_WIDTH - 20,
.policy = SCHED_NORMAL,
.cpus_ptr = &init_task.cpus_mask,
.user_cpus_ptr = NULL,
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 2c0f782a9089..ff020b99625c 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1308,6 +1308,11 @@ static void set_load_weight(struct task_struct *p, bool update_load)
}
}
+static void set_latency_weight(struct task_struct *p)
+{
+ p->se.latency_weight = sched_latency_to_weight[p->latency_prio];
+}
+
#ifdef CONFIG_UCLAMP_TASK
/*
* Serializes updates of utilization clamp values
@@ -4474,7 +4479,7 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
p->prio = current->normal_prio;
/* Propagate the parent's latency requirements to the child as well */
- p->latency_nice = current->latency_nice;
+ p->latency_prio = current->latency_prio;
uclamp_fork(p);
@@ -4492,7 +4497,9 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
p->prio = p->normal_prio = p->static_prio;
set_load_weight(p, false);
- p->latency_nice = DEFAULT_LATENCY_NICE;
+ p->latency_prio = NICE_TO_LATENCY(0);
+ set_latency_weight(p);
+
/*
* We don't need the reset flag anymore after the fork. It has
* fulfilled its duty:
@@ -7207,7 +7214,8 @@ static void __setscheduler_latency(struct task_struct *p,
const struct sched_attr *attr)
{
if (attr->sched_flags & SCHED_FLAG_LATENCY_NICE) {
- p->latency_nice = attr->sched_latency_nice;
+ p->latency_prio = NICE_TO_LATENCY(attr->sched_latency_nice);
+ set_latency_weight(p);
}
}
@@ -7341,7 +7349,7 @@ static int __sched_setscheduler(struct task_struct *p,
if (attr->sched_latency_nice < MIN_LATENCY_NICE)
return -EINVAL;
/* Use the same security checks as NICE */
- if (attr->sched_latency_nice < p->latency_nice &&
+ if (attr->sched_latency_nice < LATENCY_TO_NICE(p->latency_prio) &&
!capable(CAP_SYS_NICE))
return -EPERM;
}
@@ -7381,7 +7389,7 @@ static int __sched_setscheduler(struct task_struct *p,
if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP)
goto change;
if (attr->sched_flags & SCHED_FLAG_LATENCY_NICE &&
- attr->sched_latency_nice != p->latency_nice)
+ attr->sched_latency_nice != LATENCY_TO_NICE(p->latency_prio))
goto change;
p->sched_reset_on_fork = reset_on_fork;
@@ -7922,7 +7930,7 @@ SYSCALL_DEFINE4(sched_getattr, pid_t, pid, struct sched_attr __user *, uattr,
get_params(p, &kattr);
kattr.sched_flags &= SCHED_FLAG_ALL;
- kattr.sched_latency_nice = p->latency_nice;
+ kattr.sched_latency_nice = LATENCY_TO_NICE(p->latency_prio);
#ifdef CONFIG_UCLAMP_TASK
/*
@@ -11117,6 +11125,20 @@ const u32 sched_prio_to_wmult[40] = {
/* 15 */ 119304647, 148102320, 186737708, 238609294, 286331153,
};
+/*
+ * latency weight for wakeup preemption
+ */
+const int sched_latency_to_weight[40] = {
+ /* -20 */ 1024, 973, 922, 870, 819,
+ /* -15 */ 768, 717, 666, 614, 563,
+ /* -10 */ 512, 461, 410, 358, 307,
+ /* -5 */ 256, 205, 154, 102, 51,
+ /* 0 */ 0, -51, -102, -154, -205,
+ /* 5 */ -256, -307, -358, -410, -461,
+ /* 10 */ -512, -563, -614, -666, -717,
+ /* 15 */ -768, -819, -870, -922, -973,
+};
+
void call_trace_sched_update_nr_running(struct rq *rq, int count)
{
trace_sched_update_nr_running_tp(rq, count);
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index a3f7876217a6..06aaa0c81d4b 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -1042,7 +1042,7 @@ void proc_sched_show_task(struct task_struct *p, struct pid_namespace *ns,
#endif
P(policy);
P(prio);
- P(latency_nice);
+ P(latency_prio);
if (task_has_dl_policy(p)) {
P(dl.runtime);
P(dl.deadline);
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index bc9f6e94c84e..3af74f1a79ca 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5619,6 +5619,35 @@ static int sched_idle_cpu(int cpu)
}
#endif
+static void set_next_buddy(struct sched_entity *se);
+
+static void check_preempt_from_idle(struct cfs_rq *cfs, struct sched_entity *se)
+{
+ struct sched_entity *next;
+
+ if (se->latency_weight <= 0)
+ return;
+
+ if (cfs->nr_running <= 1)
+ return;
+ /*
+ * When waking from idle, we don't need to check to preempt at wakeup
+ * the idle thread and don't set next buddy as a candidate for being
+ * picked in priority.
+ * In case of simultaneous wakeup from idle, the latency sensitive tasks
+ * lost opportunity to preempt non sensitive tasks which woke up
+ * simultaneously.
+ */
+
+ if (cfs->next)
+ next = cfs->next;
+ else
+ next = __pick_first_entity(cfs);
+
+ if (next && wakeup_preempt_entity(next, se) == 1)
+ set_next_buddy(se);
+}
+
/*
* The enqueue_task method is called before nr_running is
* increased. Here we update the fair scheduling stats and
@@ -5712,6 +5741,9 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
if (!task_new)
update_overutilized_status(rq);
+ if (rq->curr == rq->idle)
+ check_preempt_from_idle(cfs_rq_of(&p->se), &p->se);
+
enqueue_throttle:
if (cfs_bandwidth_used()) {
/*
@@ -5733,8 +5765,6 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
hrtick_update(rq);
}
-static void set_next_buddy(struct sched_entity *se);
-
/*
* The dequeue_task method is called before nr_running is
* decreased. We remove the task from the rbtree and
@@ -6991,6 +7021,37 @@ balance_fair(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
}
#endif /* CONFIG_SMP */
+static long wakeup_latency_gran(struct sched_entity *curr, struct sched_entity *se)
+{
+ int latency_weight = se->latency_weight;
+ long thresh = sysctl_sched_latency;
+
+ /*
+ * A positive latency weigth means that the sched_entity has latency
+ * requirement that needs to be evaluated versus other entity.
+ * Otherwise, use the latency weight to evaluate how much scheduling
+ * delay is acceptable by se.
+ */
+ if ((se->latency_weight > 0) || (curr->latency_weight > 0))
+ latency_weight -= curr->latency_weight;
+
+ if (!latency_weight)
+ return 0;
+
+ if (sched_feat(GENTLE_FAIR_SLEEPERS))
+ thresh >>= 1;
+
+ /*
+ * Clamp the delta to stay in the scheduler period range
+ * [-sysctl_sched_latency:sysctl_sched_latency]
+ */
+ latency_weight = clamp_t(long, latency_weight,
+ -1 * NICE_LATENCY_WEIGHT_MAX,
+ NICE_LATENCY_WEIGHT_MAX);
+
+ return (thresh * latency_weight) >> NICE_LATENCY_SHIFT;
+}
+
static unsigned long wakeup_gran(struct sched_entity *se)
{
unsigned long gran = sysctl_sched_wakeup_granularity;
@@ -7030,6 +7091,9 @@ wakeup_preempt_entity(struct sched_entity *curr, struct sched_entity *se)
{
s64 gran, vdiff = curr->vruntime - se->vruntime;
+ /* Take into account latency priority */
+ vdiff += wakeup_latency_gran(curr, se);
+
if (vdiff <= 0)
return -1;
@@ -7138,6 +7202,7 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_
return;
update_curr(cfs_rq_of(se));
+
if (wakeup_preempt_entity(se, pse) == 1) {
/*
* Bias pick_next to pick the sched entity that is
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 271ecd37c13d..831b2c8feff1 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -134,6 +134,17 @@ extern void call_trace_sched_update_nr_running(struct rq *rq, int count);
* Default tasks should be treated as a task with latency_nice = 0.
*/
#define DEFAULT_LATENCY_NICE 0
+#define DEFAULT_LATENCY_PRIO (DEFAULT_LATENCY_NICE + LATENCY_NICE_WIDTH/2)
+
+/*
+ * Convert user-nice values [ -20 ... 0 ... 19 ]
+ * to static latency [ 0..39 ],
+ * and back.
+ */
+#define NICE_TO_LATENCY(nice) ((nice) + DEFAULT_LATENCY_PRIO)
+#define LATENCY_TO_NICE(prio) ((prio) - DEFAULT_LATENCY_PRIO)
+#define NICE_LATENCY_SHIFT (SCHED_FIXEDPOINT_SHIFT)
+#define NICE_LATENCY_WEIGHT_MAX (1L << NICE_LATENCY_SHIFT)
/*
* Increase resolution of nice-level calculations for 64-bit architectures.
@@ -2078,6 +2089,7 @@ static_assert(WF_TTWU == SD_BALANCE_WAKE);
extern const int sched_prio_to_weight[40];
extern const u32 sched_prio_to_wmult[40];
+extern const int sched_latency_to_weight[40];
/*
* {de,en}queue flags:
--
2.17.1
Powered by blists - more mailing lists