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[PATCH 0/8] sched/deadline: Return the best satisfying affinity and dl in cpudl_find

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  [PATCH 0/8] sched/deadline: Return the best satisfying affinity and dl in cpudl_find Byungchul Park <byungchul.park@lge.com> - 2017-03-23 11:40 +0100
    [PATCH 4/8] sched/deadline: Factor out the selecting of suitable max cpu Byungchul Park <byungchul.park@lge.com> - 2017-03-23 11:40 +0100
    [PATCH 3/8] sched/deadline: Add cpudl_maximum_dl() for clean-up Byungchul Park <byungchul.park@lge.com> - 2017-03-23 11:40 +0100
    [PATCH 5/8] sched/deadline: Protect read of cpudl heap with a lock Byungchul Park <byungchul.park@lge.com> - 2017-03-23 11:40 +0100
    [PATCH 2/8] sched/deadline: Re-define parameters of cpudl heapify functions Byungchul Park <byungchul.park@lge.com> - 2017-03-23 11:40 +0100
    [PATCH 6/8] sched/deadline: Don't return meaningless cpu in cpudl_maximum_cpu() Byungchul Park <byungchul.park@lge.com> - 2017-03-23 11:40 +0100
    [PATCH 7/8] sched/deadline: Factor out the modifying of cpudl's heap tree Byungchul Park <byungchul.park@lge.com> - 2017-03-23 11:40 +0100
    Re: [PATCH 0/8] sched/deadline: Return the best satisfying affinity  and dl in cpudl_find Byungchul Park <byungchul.park@lge.com> - 2017-03-23 23:40 +0100
    Re: [PATCH 0/8] sched/deadline: Return the best satisfying affinity  and dl in cpudl_find Juri Lelli <juri.lelli@arm.com> - 2017-03-27 16:10 +0200

#1607331 — [PATCH 0/8] sched/deadline: Return the best satisfying affinity and dl in cpudl_find

cpudl_find() is used to find a cpu having the latest dl. The function
should return the latest cpu among ones satisfying task's affinity and
dl constraint, but current code gives up immediately and just return
fail when it fails at the test *only with* the maximum cpu.

For example:

   cpu 0 is running a task (dl: 10).
   cpu 1 is running a task (dl: 9).
   cpu 2 is running a task (dl: 8).
   cpu 3 is running a task (dl: 2).

   where cpu 3 want to push a task (affinity is 1 2 3 and dl is 1).

In this case, the task should be migrated from cpu 3 to cpu 1, and
preempt cpu 1's task. However, current code just returns fail because
it fails at the affinity test with the maximum cpu, that is, cpu 0.

This patch set tries to find the best among ones satisfying task's
affinity and dl constraint until success or no more to see.

Byungchul Park (8):
  sched/deadline: Make find_later_rq() choose a closer cpu in topology
  sched/deadline: Re-define parameters of cpudl heapify functions
  sched/deadline: Add cpudl_maximum_dl() for clean-up
  sched/deadline: Factor out the selecting of suitable max cpu
  sched/deadline: Protect read of cpudl heap with a lock
  sched/deadline: Don't return meaningless cpu in cpudl_maximum_cpu()
  sched/deadline: Factor out the modifying of cpudl's heap tree
  sched/deadline: Return the best satisfying affinity and dl in
    cpudl_find

 kernel/sched/cpudeadline.c | 228 +++++++++++++++++++++++++++++++--------------
 kernel/sched/cpudeadline.h |   9 ++
 kernel/sched/deadline.c    |  29 +++---
 3 files changed, 182 insertions(+), 84 deletions(-)

-- 
1.9.1

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#1607332 — [PATCH 4/8] sched/deadline: Factor out the selecting of suitable max cpu

Currently, dl scheduler selects a cpu having the maximum dl on pushing.
On success, it would be a fast path, but it might fail because of the
task's affinity or dl value, so we need a slow path in case of failure.
As a first step in adding a slow path, factor out the selecting into
helper function, cpudl_fast_find().

Signed-off-by: Byungchul Park <byungchul.park@lge.com>
---
 kernel/sched/cpudeadline.c | 21 ++++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c
index f1a6ce4..f03479c 100644
--- a/kernel/sched/cpudeadline.c
+++ b/kernel/sched/cpudeadline.c
@@ -115,6 +115,19 @@ static inline u64 cpudl_maximum_dl(struct cpudl *cp)
 	return cp->elements[0].dl;
 }
 
+static int cpudl_fast_find(struct cpudl *cp, struct task_struct *p)
+{
+	const struct sched_dl_entity *dl_se = &p->dl;
+	int max_cpu = cpudl_maximum_cpu(cp);
+	u64 max_dl = cpudl_maximum_dl(cp);
+
+	if (cpumask_test_cpu(max_cpu, &p->cpus_allowed) &&
+	    dl_time_before(dl_se->deadline, max_dl))
+		return max_cpu;
+
+	return -1;
+}
+
 /*
  * cpudl_find - find the best (later-dl) CPU in the system
  * @cp: the cpudl max-heap context
@@ -127,16 +140,14 @@ int cpudl_find(struct cpudl *cp, struct task_struct *p,
 	       struct cpumask *later_mask)
 {
 	int best_cpu = -1;
-	const struct sched_dl_entity *dl_se = &p->dl;
 
 	if (later_mask &&
 	    cpumask_and(later_mask, cp->free_cpus, &p->cpus_allowed)) {
 		best_cpu = cpumask_any(later_mask);
 		goto out;
-	} else if (cpumask_test_cpu(cpudl_maximum_cpu(cp), &p->cpus_allowed) &&
-			dl_time_before(dl_se->deadline, cpudl_maximum_dl(cp))) {
-		best_cpu = cpudl_maximum_cpu(cp);
-		if (later_mask)
+	} else {
+		best_cpu = cpudl_fast_find(cp, p);
+		if (best_cpu != -1 && later_mask)
 			cpumask_set_cpu(best_cpu, later_mask);
 	}
 
-- 
1.9.1

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#1607333 — [PATCH 3/8] sched/deadline: Add cpudl_maximum_dl() for clean-up

Current code uses cpudl_maximum() to get the root node's cpu, while it
directly accesses the root node using 'cp->elements[0].dl' to get the
root node's dl. It would be better and more readible if a function to
get the dl is added. So add it.

Signed-off-by: Byungchul Park <byungchul.park@lge.com>
---
 kernel/sched/cpudeadline.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c
index 7dd6d9d..f1a6ce4 100644
--- a/kernel/sched/cpudeadline.c
+++ b/kernel/sched/cpudeadline.c
@@ -105,11 +105,16 @@ static void cpudl_heapify(struct cpudl_item *e, int size, int idx)
 		cpudl_heapify_down(e, size, idx);
 }
 
-static inline int cpudl_maximum(struct cpudl *cp)
+static inline int cpudl_maximum_cpu(struct cpudl *cp)
 {
 	return cp->elements[0].cpu;
 }
 
+static inline u64 cpudl_maximum_dl(struct cpudl *cp)
+{
+	return cp->elements[0].dl;
+}
+
 /*
  * cpudl_find - find the best (later-dl) CPU in the system
  * @cp: the cpudl max-heap context
@@ -128,9 +133,9 @@ int cpudl_find(struct cpudl *cp, struct task_struct *p,
 	    cpumask_and(later_mask, cp->free_cpus, &p->cpus_allowed)) {
 		best_cpu = cpumask_any(later_mask);
 		goto out;
-	} else if (cpumask_test_cpu(cpudl_maximum(cp), &p->cpus_allowed) &&
-			dl_time_before(dl_se->deadline, cp->elements[0].dl)) {
-		best_cpu = cpudl_maximum(cp);
+	} else if (cpumask_test_cpu(cpudl_maximum_cpu(cp), &p->cpus_allowed) &&
+			dl_time_before(dl_se->deadline, cpudl_maximum_dl(cp))) {
+		best_cpu = cpudl_maximum_cpu(cp);
 		if (later_mask)
 			cpumask_set_cpu(best_cpu, later_mask);
 	}
-- 
1.9.1

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#1607336 — [PATCH 5/8] sched/deadline: Protect read of cpudl heap with a lock

Current code reads cp->elements[0].cpu and cp->elements[0].dl without
acquiring cpudl's lock. There are two problems on it:

   1. When we read elements[0].dl, the value can be broken on 32 bit
      machine because elements[0].dl is 64 bit data. We should guarantee
      it to be done atomically.

   2. Obsolete data can be read unless syncronizing with updaters:

      updater1      updater2      reader
      --------      --------      ------
      lock A
      set maxcpu = cpu1
      unlock A
                    lock A
                    set maxcpu = cpu2
                    unlock A
                                  read maxcpu, it might be -1

      where maxcpu was -1 initially.

When reading maxcpu, the value might be -1, we expect that should be
cpu2 though. So force readers also to be protected using the lock.

Signed-off-by: Byungchul Park <byungchul.park@lge.com>
---
 kernel/sched/cpudeadline.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c
index f03479c..37bbb66 100644
--- a/kernel/sched/cpudeadline.c
+++ b/kernel/sched/cpudeadline.c
@@ -118,8 +118,14 @@ static inline u64 cpudl_maximum_dl(struct cpudl *cp)
 static int cpudl_fast_find(struct cpudl *cp, struct task_struct *p)
 {
 	const struct sched_dl_entity *dl_se = &p->dl;
-	int max_cpu = cpudl_maximum_cpu(cp);
-	u64 max_dl = cpudl_maximum_dl(cp);
+	unsigned long flags;
+	int max_cpu;
+	u64 max_dl;
+
+	raw_spin_lock_irqsave(&cp->lock, flags);
+	max_cpu = cpudl_maximum_cpu(cp);
+	max_dl = cpudl_maximum_dl(cp);
+	raw_spin_unlock_irqrestore(&cp->lock, flags);
 
 	if (cpumask_test_cpu(max_cpu, &p->cpus_allowed) &&
 	    dl_time_before(dl_se->deadline, max_dl))
-- 
1.9.1

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#1607337 — [PATCH 2/8] sched/deadline: Re-define parameters of cpudl heapify functions

If you don't like this clean-up patch, please let me know. If so, I will
exclude this patch from next spin.

Thank you,
Byungchul

-----8<-----
From b303ccf6b64064ce22aa17d16a012dcc7904ad32 Mon Sep 17 00:00:00 2001
From: Byungchul Park <byungchul.park@lge.com>
Date: Wed, 22 Mar 2017 14:07:22 +0900
Subject: [PATCH 2/8] sched/deadline: Re-define parameters of cpudl heapify
 functions

Currently whole 'struct cpudl' is used as a parameter on heapifying.
However, only elements and size are needed on the work. So change the
parameters.

Signed-off-by: Byungchul Park <byungchul.park@lge.com>
---
 kernel/sched/cpudeadline.c | 63 ++++++++++++++++++++++------------------------
 1 file changed, 30 insertions(+), 33 deletions(-)

diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c
index fba235c..7dd6d9d 100644
--- a/kernel/sched/cpudeadline.c
+++ b/kernel/sched/cpudeadline.c
@@ -31,14 +31,14 @@ static inline int right_child(int i)
 	return (i << 1) + 2;
 }
 
-static void cpudl_heapify_down(struct cpudl *cp, int idx)
+static void cpudl_heapify_down(struct cpudl_item *e, int size, int idx)
 {
 	int l, r, largest;
 
-	int orig_cpu = cp->elements[idx].cpu;
-	u64 orig_dl = cp->elements[idx].dl;
+	int orig_cpu = e[idx].cpu;
+	u64 orig_dl = e[idx].dl;
 
-	if (left_child(idx) >= cp->size)
+	if (left_child(idx) >= size)
 		return;
 
 	/* adapted from lib/prio_heap.c */
@@ -49,63 +49,60 @@ static void cpudl_heapify_down(struct cpudl *cp, int idx)
 		largest = idx;
 		largest_dl = orig_dl;
 
-		if ((l < cp->size) && dl_time_before(orig_dl,
-						cp->elements[l].dl)) {
+		if ((l < size) && dl_time_before(orig_dl, e[l].dl)) {
 			largest = l;
-			largest_dl = cp->elements[l].dl;
+			largest_dl = e[l].dl;
 		}
-		if ((r < cp->size) && dl_time_before(largest_dl,
-						cp->elements[r].dl))
+		if ((r < size) && dl_time_before(largest_dl, e[r].dl))
 			largest = r;
 
 		if (largest == idx)
 			break;
 
 		/* pull largest child onto idx */
-		cp->elements[idx].cpu = cp->elements[largest].cpu;
-		cp->elements[idx].dl = cp->elements[largest].dl;
-		cp->elements[cp->elements[idx].cpu].idx = idx;
+		e[idx].cpu = e[largest].cpu;
+		e[idx].dl = e[largest].dl;
+		e[e[idx].cpu].idx = idx;
 		idx = largest;
 	}
 	/* actual push down of saved original values orig_* */
-	cp->elements[idx].cpu = orig_cpu;
-	cp->elements[idx].dl = orig_dl;
-	cp->elements[cp->elements[idx].cpu].idx = idx;
+	e[idx].cpu = orig_cpu;
+	e[idx].dl = orig_dl;
+	e[e[idx].cpu].idx = idx;
 }
 
-static void cpudl_heapify_up(struct cpudl *cp, int idx)
+static void cpudl_heapify_up(struct cpudl_item *e, int size, int idx)
 {
 	int p;
 
-	int orig_cpu = cp->elements[idx].cpu;
-	u64 orig_dl = cp->elements[idx].dl;
+	int orig_cpu = e[idx].cpu;
+	u64 orig_dl = e[idx].dl;
 
 	if (idx == 0)
 		return;
 
 	do {
 		p = parent(idx);
-		if (dl_time_before(orig_dl, cp->elements[p].dl))
+		if (dl_time_before(orig_dl, e[p].dl))
 			break;
 		/* pull parent onto idx */
-		cp->elements[idx].cpu = cp->elements[p].cpu;
-		cp->elements[idx].dl = cp->elements[p].dl;
-		cp->elements[cp->elements[idx].cpu].idx = idx;
+		e[idx].cpu = e[p].cpu;
+		e[idx].dl = e[p].dl;
+		e[e[idx].cpu].idx = idx;
 		idx = p;
 	} while (idx != 0);
 	/* actual push up of saved original values orig_* */
-	cp->elements[idx].cpu = orig_cpu;
-	cp->elements[idx].dl = orig_dl;
-	cp->elements[cp->elements[idx].cpu].idx = idx;
+	e[idx].cpu = orig_cpu;
+	e[idx].dl = orig_dl;
+	e[e[idx].cpu].idx = idx;
 }
 
-static void cpudl_heapify(struct cpudl *cp, int idx)
+static void cpudl_heapify(struct cpudl_item *e, int size, int idx)
 {
-	if (idx > 0 && dl_time_before(cp->elements[parent(idx)].dl,
-				cp->elements[idx].dl))
-		cpudl_heapify_up(cp, idx);
+	if (idx > 0 && dl_time_before(e[parent(idx)].dl, e[idx].dl))
+		cpudl_heapify_up(e, size, idx);
 	else
-		cpudl_heapify_down(cp, idx);
+		cpudl_heapify_down(e, size, idx);
 }
 
 static inline int cpudl_maximum(struct cpudl *cp)
@@ -176,7 +173,7 @@ void cpudl_clear(struct cpudl *cp, int cpu)
 		cp->size--;
 		cp->elements[new_cpu].idx = old_idx;
 		cp->elements[cpu].idx = IDX_INVALID;
-		cpudl_heapify(cp, old_idx);
+		cpudl_heapify(cp->elements, cp->size, old_idx);
 
 		cpumask_set_cpu(cpu, cp->free_cpus);
 	}
@@ -208,11 +205,11 @@ void cpudl_set(struct cpudl *cp, int cpu, u64 dl)
 		cp->elements[new_idx].dl = dl;
 		cp->elements[new_idx].cpu = cpu;
 		cp->elements[cpu].idx = new_idx;
-		cpudl_heapify_up(cp, new_idx);
+		cpudl_heapify_up(cp->elements, cp->size, new_idx);
 		cpumask_clear_cpu(cpu, cp->free_cpus);
 	} else {
 		cp->elements[old_idx].dl = dl;
-		cpudl_heapify(cp, old_idx);
+		cpudl_heapify(cp->elements, cp->size, old_idx);
 	}
 
 	raw_spin_unlock_irqrestore(&cp->lock, flags);
-- 
1.9.1

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#1607339 — [PATCH 6/8] sched/deadline: Don't return meaningless cpu in cpudl_maximum_cpu()

When the heap tree is empty, cp->elements[0].cpu has meaningless value.
We need to consider the case.

Signed-off-by: Byungchul Park <byungchul.park@lge.com>
---
 kernel/sched/cpudeadline.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c
index 37bbb66..21404b8 100644
--- a/kernel/sched/cpudeadline.c
+++ b/kernel/sched/cpudeadline.c
@@ -107,7 +107,8 @@ static void cpudl_heapify(struct cpudl_item *e, int size, int idx)
 
 static inline int cpudl_maximum_cpu(struct cpudl *cp)
 {
-	return cp->elements[0].cpu;
+	int cpu = cp->elements[0].cpu;
+	return cp->elements[cpu].idx == IDX_INVALID ? -1 : cpu;
 }
 
 static inline u64 cpudl_maximum_dl(struct cpudl *cp)
@@ -127,7 +128,8 @@ static int cpudl_fast_find(struct cpudl *cp, struct task_struct *p)
 	max_dl = cpudl_maximum_dl(cp);
 	raw_spin_unlock_irqrestore(&cp->lock, flags);
 
-	if (cpumask_test_cpu(max_cpu, &p->cpus_allowed) &&
+	if (max_cpu != -1 &&
+	    cpumask_test_cpu(max_cpu, &p->cpus_allowed) &&
 	    dl_time_before(dl_se->deadline, max_dl))
 		return max_cpu;
 
-- 
1.9.1

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#1607340 — [PATCH 7/8] sched/deadline: Factor out the modifying of cpudl's heap tree

Currently, cpudl_{set,clear} is responsible for manipulating cpudl's
heap tree and free_cpus list under lock protection. However, operation
manipulating the heap tree itself is reusable.

Actually, the operation is useful when picking up the second maximum
node from the tree, where it does not need to manipulate free_cpus list
but only needs to manipulate the tree.

Signed-off-by: Byungchul Park <byungchul.park@lge.com>
---
 kernel/sched/cpudeadline.c | 95 ++++++++++++++++++++++++++++++----------------
 1 file changed, 62 insertions(+), 33 deletions(-)

diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c
index 21404b8..453159a 100644
--- a/kernel/sched/cpudeadline.c
+++ b/kernel/sched/cpudeadline.c
@@ -116,6 +116,64 @@ static inline u64 cpudl_maximum_dl(struct cpudl *cp)
 	return cp->elements[0].dl;
 }
 
+/*
+ * __cpudl_clear - remove a cpu from the cpudl max-heap
+ * @cp: the cpudl max-heap context
+ * @cpu: the target cpu
+ *
+ * Notes: assumes cpu_rq(cpu)->lock and cpudl->lock are locked
+ *
+ * Returns: (void)
+ */
+static void __cpudl_clear(struct cpudl *cp, int cpu)
+{
+	int old_idx, new_cpu;
+
+	old_idx = cp->elements[cpu].idx;
+	if (old_idx == IDX_INVALID) {
+		/*
+		 * Nothing to remove if old_idx was invalid.
+		 * This could happen if a rq_offline_dl is
+		 * called for a CPU without -dl tasks running.
+		 */
+	} else {
+		new_cpu = cp->elements[cp->size - 1].cpu;
+		cp->elements[old_idx].dl = cp->elements[cp->size - 1].dl;
+		cp->elements[old_idx].cpu = new_cpu;
+		cp->size--;
+		cp->elements[new_cpu].idx = old_idx;
+		cp->elements[cpu].idx = IDX_INVALID;
+		cpudl_heapify(cp->elements, cp->size, old_idx);
+	}
+}
+
+/*
+ * __cpudl_set - update the cpudl max-heap
+ * @cp: the cpudl max-heap context
+ * @cpu: the target cpu
+ * @dl: the new earliest deadline for this cpu
+ *
+ * Notes: assumes cpu_rq(cpu)->lock and cpudl->lock are locked
+ *
+ * Returns: (void)
+ */
+static void __cpudl_set(struct cpudl *cp, int cpu, u64 dl)
+{
+	int old_idx;
+
+	old_idx = cp->elements[cpu].idx;
+	if (old_idx == IDX_INVALID) {
+		int new_idx = cp->size++;
+		cp->elements[new_idx].dl = dl;
+		cp->elements[new_idx].cpu = cpu;
+		cp->elements[cpu].idx = new_idx;
+		cpudl_heapify_up(cp->elements, cp->size, new_idx);
+	} else {
+		cp->elements[old_idx].dl = dl;
+		cpudl_heapify(cp->elements, cp->size, old_idx);
+	}
+}
+
 static int cpudl_fast_find(struct cpudl *cp, struct task_struct *p)
 {
 	const struct sched_dl_entity *dl_se = &p->dl;
@@ -176,31 +234,14 @@ int cpudl_find(struct cpudl *cp, struct task_struct *p,
  */
 void cpudl_clear(struct cpudl *cp, int cpu)
 {
-	int old_idx, new_cpu;
 	unsigned long flags;
 
 	WARN_ON(!cpu_present(cpu));
 
 	raw_spin_lock_irqsave(&cp->lock, flags);
-
-	old_idx = cp->elements[cpu].idx;
-	if (old_idx == IDX_INVALID) {
-		/*
-		 * Nothing to remove if old_idx was invalid.
-		 * This could happen if a rq_offline_dl is
-		 * called for a CPU without -dl tasks running.
-		 */
-	} else {
-		new_cpu = cp->elements[cp->size - 1].cpu;
-		cp->elements[old_idx].dl = cp->elements[cp->size - 1].dl;
-		cp->elements[old_idx].cpu = new_cpu;
-		cp->size--;
-		cp->elements[new_cpu].idx = old_idx;
-		cp->elements[cpu].idx = IDX_INVALID;
-		cpudl_heapify(cp->elements, cp->size, old_idx);
-
+	__cpudl_clear(cp, cpu);
+	if (cp->elements[cpu].idx != IDX_INVALID)
 		cpumask_set_cpu(cpu, cp->free_cpus);
-	}
 	raw_spin_unlock_irqrestore(&cp->lock, flags);
 }
 
@@ -216,26 +257,14 @@ void cpudl_clear(struct cpudl *cp, int cpu)
  */
 void cpudl_set(struct cpudl *cp, int cpu, u64 dl)
 {
-	int old_idx;
 	unsigned long flags;
 
 	WARN_ON(!cpu_present(cpu));
 
 	raw_spin_lock_irqsave(&cp->lock, flags);
-
-	old_idx = cp->elements[cpu].idx;
-	if (old_idx == IDX_INVALID) {
-		int new_idx = cp->size++;
-		cp->elements[new_idx].dl = dl;
-		cp->elements[new_idx].cpu = cpu;
-		cp->elements[cpu].idx = new_idx;
-		cpudl_heapify_up(cp->elements, cp->size, new_idx);
+	__cpudl_set(cp, cpu, dl);
+	if (cp->elements[cpu].idx == IDX_INVALID)
 		cpumask_clear_cpu(cpu, cp->free_cpus);
-	} else {
-		cp->elements[old_idx].dl = dl;
-		cpudl_heapify(cp->elements, cp->size, old_idx);
-	}
-
 	raw_spin_unlock_irqrestore(&cp->lock, flags);
 }
 
-- 
1.9.1

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#1607996 — Re: [PATCH 0/8] sched/deadline: Return the best satisfying affinity and dl in cpudl_find

On Thu, Mar 23, 2017 at 07:32:35PM +0900, Byungchul Park wrote:
> cpudl_find() is used to find a cpu having the latest dl. The function
> should return the latest cpu among ones satisfying task's affinity and
> dl constraint, but current code gives up immediately and just return
> fail when it fails at the test *only with* the maximum cpu.
> 
> For example:
> 
>    cpu 0 is running a task (dl: 10).
>    cpu 1 is running a task (dl: 9).
>    cpu 2 is running a task (dl: 8).
>    cpu 3 is running a task (dl: 2).
                                  ^
                              should be 1
> 
>    where cpu 3 want to push a task (affinity is 1 2 3 and dl is 1).
                                                                  ^
                                                        should be 2
> 
> In this case, the task should be migrated from cpu 3 to cpu 1, and
> preempt cpu 1's task. However, current code just returns fail because
> it fails at the affinity test with the maximum cpu, that is, cpu 0.
> 
> This patch set tries to find the best among ones satisfying task's
> affinity and dl constraint until success or no more to see.
> 
> Byungchul Park (8):
>   sched/deadline: Make find_later_rq() choose a closer cpu in topology
>   sched/deadline: Re-define parameters of cpudl heapify functions
>   sched/deadline: Add cpudl_maximum_dl() for clean-up
>   sched/deadline: Factor out the selecting of suitable max cpu
>   sched/deadline: Protect read of cpudl heap with a lock
>   sched/deadline: Don't return meaningless cpu in cpudl_maximum_cpu()
>   sched/deadline: Factor out the modifying of cpudl's heap tree
>   sched/deadline: Return the best satisfying affinity and dl in
>     cpudl_find
> 
>  kernel/sched/cpudeadline.c | 228 +++++++++++++++++++++++++++++++--------------
>  kernel/sched/cpudeadline.h |   9 ++
>  kernel/sched/deadline.c    |  29 +++---
>  3 files changed, 182 insertions(+), 84 deletions(-)
> 
> -- 
> 1.9.1

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#1609863 — Re: [PATCH 0/8] sched/deadline: Return the best satisfying affinity and dl in cpudl_find

Hi,

On 23/03/17 19:32, Byungchul Park wrote:
> cpudl_find() is used to find a cpu having the latest dl. The function
> should return the latest cpu among ones satisfying task's affinity and
> dl constraint, but current code gives up immediately and just return
> fail when it fails at the test *only with* the maximum cpu.
> 
> For example:
> 
>    cpu 0 is running a task (dl: 10).
>    cpu 1 is running a task (dl: 9).
>    cpu 2 is running a task (dl: 8).
>    cpu 3 is running a task (dl: 2).
> 
>    where cpu 3 want to push a task (affinity is 1 2 3 and dl is 1).

Hummm, but this should only happen if you disable admission control,
right? Otherwise task's affinity can't be smaller that 0-3.

> 
> In this case, the task should be migrated from cpu 3 to cpu 1, and
> preempt cpu 1's task. However, current code just returns fail because
> it fails at the affinity test with the maximum cpu, that is, cpu 0.
> 
> This patch set tries to find the best among ones satisfying task's
> affinity and dl constraint until success or no more to see.
> 

Anyway, do you have numbers showing how common is you fail scenario?
It would be interesting to understand how much the slow path is actually
used, IMHO.

Thanks,

- Juri

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