Improve a few aspects of directed convergence, which problems
have become more visible with the improved (and thus more
aggressive) task-flipping code.
We also have the new 'cpupid' sharing info which converges more
precisely and thus highlights weaknesses in group balancing more
visibly:
- We should only balance over buddy groups that are smaller
than the other (not fully filled) buddy groups
- Do not 'spread' buddy groups that fully fill a node
- Do not 'spread' singular buddy groups
These bugs were prominently visible with certain preemption
options and timings with the previous code as well, so this
is a regression fix as well.
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: Peter Zijlstra <a.p.zijls...@chello.nl>
Cc: Andrea Arcangeli <aarca...@redhat.com>
Cc: Rik van Riel <r...@redhat.com>
Cc: Mel Gorman <mgor...@suse.de>
Cc: Hugh Dickins <hu...@google.com>
Signed-off-by: Ingo Molnar <mi...@kernel.org>
---
kernel/sched/fair.c | 101 ++++++++++++++++++++++++++++++++++++----------------
1 file changed, 71 insertions(+), 30 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index fd49920..c393fba 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -926,6 +926,7 @@ static long calc_node_load(int node, bool use_higher)
long cpu_load_highfreq;
long cpu_load_lowfreq;
long cpu_load_curr;
+ long cpu_load_numa;
long min_cpu_load;
long max_cpu_load;
long node_load;
@@ -935,18 +936,22 @@ static long calc_node_load(int node, bool use_higher)
for_each_cpu(cpu, cpumask_of_node(node)) {
struct rq *rq = cpu_rq(cpu);
+ long cpu_load;
+ cpu_load_numa = rq->numa_weight;
cpu_load_curr = rq->load.weight;
cpu_load_lowfreq = rq->cpu_load[NUMA_LOAD_IDX_LOWFREQ];
cpu_load_highfreq = rq->cpu_load[NUMA_LOAD_IDX_HIGHFREQ];
- min_cpu_load = min(min(cpu_load_curr, cpu_load_lowfreq),
cpu_load_highfreq);
- max_cpu_load = max(max(cpu_load_curr, cpu_load_lowfreq),
cpu_load_highfreq);
+ min_cpu_load = min(min(min(cpu_load_numa, cpu_load_curr),
cpu_load_lowfreq), cpu_load_highfreq);
+ max_cpu_load = max(max(max(cpu_load_numa, cpu_load_curr),
cpu_load_lowfreq), cpu_load_highfreq);
if (use_higher)
- node_load += max_cpu_load;
+ cpu_load = max_cpu_load;
else
- node_load += min_cpu_load;
+ cpu_load = min_cpu_load;
+
+ node_load += cpu_load;
}
return node_load;
@@ -1087,6 +1092,7 @@ static int find_intranode_imbalance(int this_node, int
this_cpu)
long cpu_load_lowfreq;
long this_cpu_load;
long cpu_load_curr;
+ long cpu_load_numa;
long min_cpu_load;
long cpu_load;
int min_cpu;
@@ -1102,14 +1108,15 @@ static int find_intranode_imbalance(int this_node, int
this_cpu)
for_each_cpu(cpu, cpumask_of_node(this_node)) {
struct rq *rq = cpu_rq(cpu);
+ cpu_load_numa = rq->numa_weight;
cpu_load_curr = rq->load.weight;
cpu_load_lowfreq = rq->cpu_load[NUMA_LOAD_IDX_LOWFREQ];
cpu_load_highfreq = rq->cpu_load[NUMA_LOAD_IDX_HIGHFREQ];
- if (cpu == this_cpu) {
- this_cpu_load = min(min(cpu_load_curr,
cpu_load_lowfreq), cpu_load_highfreq);
- }
- cpu_load = max(max(cpu_load_curr, cpu_load_lowfreq),
cpu_load_highfreq);
+ if (cpu == this_cpu)
+ this_cpu_load = min(min(min(cpu_load_numa,
cpu_load_curr), cpu_load_lowfreq), cpu_load_highfreq);
+
+ cpu_load = max(max(max(cpu_load_numa, cpu_load_curr),
cpu_load_lowfreq), cpu_load_highfreq);
/* Find the idlest CPU: */
if (cpu_load < min_cpu_load) {
@@ -1128,16 +1135,18 @@ static int find_intranode_imbalance(int this_node, int
this_cpu)
/*
* Search a node for the smallest-group task and return
* it plus the size of the group it is in.
+ *
+ * TODO: can be done with a single pass.
*/
-static int buddy_group_size(int node, struct task_struct *p)
+static int buddy_group_size(int node, struct task_struct *p, bool *our_group_p)
{
const cpumask_t *node_cpus_mask = cpumask_of_node(node);
cpumask_t cpus_to_check_mask;
- bool our_group_found;
+ bool buddies_group_found;
int cpu1, cpu2;
cpumask_copy(&cpus_to_check_mask, node_cpus_mask);
- our_group_found = false;
+ buddies_group_found = false;
if (WARN_ON_ONCE(cpumask_empty(&cpus_to_check_mask)))
return 0;
@@ -1156,7 +1165,12 @@ static int buddy_group_size(int node, struct task_struct
*p)
group_size = 1;
if (tasks_buddies(group_head, p))
- our_group_found = true;
+ buddies_group_found = true;
+
+ if (group_head == p) {
+ *our_group_p = true;
+ buddies_group_found = true;
+ }
/* Non-NUMA-shared tasks are 1-task groups: */
if (task_numa_shared(group_head) != 1)
@@ -1169,21 +1183,22 @@ static int buddy_group_size(int node, struct
task_struct *p)
struct task_struct *p2 = rq2->curr;
WARN_ON_ONCE(rq1 == rq2);
+ if (p2 == p)
+ *our_group_p = true;
if (tasks_buddies(group_head, p2)) {
/* 'group_head' and 'rq2->curr' are in
the same group: */
cpumask_clear_cpu(cpu2,
&cpus_to_check_mask);
group_size++;
if (tasks_buddies(p2, p))
- our_group_found = true;
+ buddies_group_found = true;
}
}
next:
-
/*
* If we just found our group and checked all
* node local CPUs then return the result:
*/
- if (our_group_found)
+ if (buddies_group_found)
return group_size;
}
} while (!cpumask_empty(&cpus_to_check_mask));
@@ -1261,8 +1276,15 @@ pick_non_numa_task:
return min_group_cpu;
}
-static int find_max_node(struct task_struct *p, int *our_group_size)
+/*
+ * Find the node with the biggest buddy group of ours, but exclude
+ * our own local group on this node and also exclude fully filled
+ * nodes:
+ */
+static int
+find_max_node(struct task_struct *p, int *our_group_size_p, int
*max_group_size_p, int full_size)
{
+ bool our_group = false;
int max_group_size;
int group_size;
int max_node;
@@ -1272,9 +1294,12 @@ static int find_max_node(struct task_struct *p, int
*our_group_size)
max_node = -1;
for_each_node(node) {
- int full_size = cpumask_weight(cpumask_of_node(node));
- group_size = buddy_group_size(node, p);
+ group_size = buddy_group_size(node, p, &our_group);
+ if (our_group) {
+ our_group = false;
+ *our_group_size_p = group_size;
+ }
if (group_size == full_size)
continue;
@@ -1284,7 +1309,7 @@ static int find_max_node(struct task_struct *p, int
*our_group_size)
}
}
- *our_group_size = max_group_size;
+ *max_group_size_p = max_group_size;
return max_node;
}
@@ -1460,19 +1485,23 @@ static int find_max_node(struct task_struct *p, int
*our_group_size)
*/
static int improve_group_balance_compress(struct task_struct *p, int this_cpu,
int this_node)
{
- int our_group_size = -1;
+ int full_size = cpumask_weight(cpumask_of_node(this_node));
+ int max_group_size = -1;
int min_group_size = -1;
+ int our_group_size = -1;
int max_node;
int min_cpu;
if (!sched_feat(NUMA_GROUP_LB_COMPRESS))
return -1;
- max_node = find_max_node(p, &our_group_size);
+ max_node = find_max_node(p, &our_group_size, &max_group_size,
full_size);
if (max_node == -1)
return -1;
+ if (our_group_size == -1)
+ return -1;
- if (WARN_ON_ONCE(our_group_size == -1))
+ if (our_group_size == full_size || our_group_size > max_group_size)
return -1;
/* We are already in the right spot: */
@@ -1517,6 +1546,7 @@ static int improve_group_balance_spread(struct
task_struct *p, int this_cpu, int
long this_node_load = -1;
long delta_load_before;
long delta_load_after;
+ int group_count = 0;
int idlest_cpu = -1;
int cpu1, cpu2;
@@ -1585,6 +1615,7 @@ static int improve_group_balance_spread(struct
task_struct *p, int this_cpu, int
min_group_size = group_size;
else
min_group_size = min(group_size,
min_group_size);
+ group_count++;
}
} while (!cpumask_empty(&cpus_to_check_mask));
@@ -1594,13 +1625,23 @@ static int improve_group_balance_spread(struct
task_struct *p, int this_cpu, int
*/
if (!found_our_group)
return -1;
+
if (!our_group_smallest)
return -1;
+
if (WARN_ON_ONCE(min_group_size == -1))
return -1;
if (WARN_ON_ONCE(our_group_size == -1))
return -1;
+ /* Since the current task is shared, this should not happen: */
+ if (WARN_ON_ONCE(group_count < 1))
+ return -1;
+
+ /* No point in moving if we are a single group: */
+ if (group_count <= 1)
+ return -1;
+
idlest_node = find_idlest_node(&idlest_cpu);
if (idlest_node == -1)
return -1;
@@ -1622,7 +1663,7 @@ static int improve_group_balance_spread(struct
task_struct *p, int this_cpu, int
*/
delta_load_before = this_node_load - idlest_node_load;
delta_load_after = (this_node_load-this_group_load) -
(idlest_node_load+this_group_load);
-
+
if (abs(delta_load_after)+SCHED_LOAD_SCALE > abs(delta_load_before))
return -1;
@@ -1806,7 +1847,7 @@ static int sched_update_ideal_cpu_shared(struct
task_struct *p, int *flip_tasks)
this_node_capacity = calc_node_capacity(this_node);
this_node_overloaded = false;
- if (this_node_load > this_node_capacity + 512)
+ if (this_node_load > this_node_capacity + SCHED_LOAD_SCALE/2)
this_node_overloaded = true;
/* If we'd stay within this node then stay put: */
@@ -1922,7 +1963,7 @@ static int sched_update_ideal_cpu_private(struct
task_struct *p)
this_node_capacity = calc_node_capacity(this_node);
this_node_overloaded = false;
- if (this_node_load > this_node_capacity + 512)
+ if (this_node_load > this_node_capacity + SCHED_LOAD_SCALE/2)
this_node_overloaded = true;
if (this_node == min_node)
@@ -1934,8 +1975,8 @@ static int sched_update_ideal_cpu_private(struct
task_struct *p)
WARN_ON_ONCE(max_node_load < min_node_load);
- /* Is the load difference at least 125% of one standard task load? */
- if (this_node_load - min_node_load < 1536)
+ /* Is the load difference at least 150% of one standard task load? */
+ if (this_node_load - min_node_load < SCHED_LOAD_SCALE*3/2)
goto out_check_intranode;
/*
@@ -5476,7 +5517,7 @@ static bool yield_to_task_fair(struct rq *rq, struct
task_struct *p, bool preemp
*
* The adjacency matrix of the resulting graph is given by:
*
- * log_2 n
+ * log_2 n
* A_i,j = \Union (i % 2^k == 0) && i / 2^(k+1) == j / 2^(k+1) (6)
* k = 0
*
@@ -5522,7 +5563,7 @@ static bool yield_to_task_fair(struct rq *rq, struct
task_struct *p, bool preemp
*
* [XXX write more on how we solve this.. _after_ merging pjt's patches that
* rewrite all of this once again.]
- */
+ */
static unsigned long __read_mostly max_load_balance_interval = HZ/10;
@@ -6133,7 +6174,7 @@ void update_group_power(struct sched_domain *sd, int cpu)
/*
* !SD_OVERLAP domains can assume that child groups
* span the current group.
- */
+ */
group = child->groups;
do {
--
1.7.11.7
--
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