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sched: Allow for overlapping sched_domain spans
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Allow for sched_domain spans that overlap by giving such domains their
own sched_group list instead of sharing the sched_groups amongst
each-other.

This is needed for machines with more than 16 nodes, because
sched_domain_node_span() will generate a node mask from the
16 nearest nodes without regard if these masks have any overlap.

Currently sched_domains have a sched_group that maps to their child
sched_domain span, and since there is no overlap we share the
sched_group between the sched_domains of the various CPUs. If however
there is overlap, we would need to link the sched_group list in
different ways for each cpu, and hence sharing isn't possible.

In order to solve this, allocate private sched_groups for each CPU's
sched_domain but have the sched_groups share a sched_group_power
structure such that we can uniquely track the power.

Reported-and-tested-by: Anton Blanchard <[email protected]>
Signed-off-by: Peter Zijlstra <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Andrew Morton <[email protected]>
Link: http://lkml.kernel.org/n/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
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Peter Zijlstra authored and Ingo Molnar committed Jul 20, 2011
1 parent 9c3f75c commit e3589f6
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Showing 3 changed files with 132 additions and 29 deletions.
2 changes: 2 additions & 0 deletions include/linux/sched.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -844,6 +844,7 @@ enum cpu_idle_type {
#define SD_SERIALIZE 0x0400 /* Only a single load balancing instance */
#define SD_ASYM_PACKING 0x0800 /* Place busy groups earlier in the domain */
#define SD_PREFER_SIBLING 0x1000 /* Prefer to place tasks in a sibling domain */
#define SD_OVERLAP 0x2000 /* sched_domains of this level overlap */

enum powersavings_balance_level {
POWERSAVINGS_BALANCE_NONE = 0, /* No power saving load balance */
Expand Down Expand Up @@ -894,6 +895,7 @@ static inline int sd_power_saving_flags(void)
}

struct sched_group_power {
atomic_t ref;
/*
* CPU power of this group, SCHED_LOAD_SCALE being max power for a
* single CPU.
Expand Down
157 changes: 128 additions & 29 deletions kernel/sched.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -6774,10 +6774,36 @@ static struct root_domain *alloc_rootdomain(void)
return rd;
}

static void free_sched_groups(struct sched_group *sg, int free_sgp)
{
struct sched_group *tmp, *first;

if (!sg)
return;

first = sg;
do {
tmp = sg->next;

if (free_sgp && atomic_dec_and_test(&sg->sgp->ref))
kfree(sg->sgp);

kfree(sg);
sg = tmp;
} while (sg != first);
}

static void free_sched_domain(struct rcu_head *rcu)
{
struct sched_domain *sd = container_of(rcu, struct sched_domain, rcu);
if (atomic_dec_and_test(&sd->groups->ref)) {

/*
* If its an overlapping domain it has private groups, iterate and
* nuke them all.
*/
if (sd->flags & SD_OVERLAP) {
free_sched_groups(sd->groups, 1);
} else if (atomic_dec_and_test(&sd->groups->ref)) {
kfree(sd->groups->sgp);
kfree(sd->groups);
}
Expand Down Expand Up @@ -6967,15 +6993,73 @@ struct sched_domain_topology_level;
typedef struct sched_domain *(*sched_domain_init_f)(struct sched_domain_topology_level *tl, int cpu);
typedef const struct cpumask *(*sched_domain_mask_f)(int cpu);

#define SDTL_OVERLAP 0x01

struct sched_domain_topology_level {
sched_domain_init_f init;
sched_domain_mask_f mask;
int flags;
struct sd_data data;
};

/*
* Assumes the sched_domain tree is fully constructed
*/
static int
build_overlap_sched_groups(struct sched_domain *sd, int cpu)
{
struct sched_group *first = NULL, *last = NULL, *groups = NULL, *sg;
const struct cpumask *span = sched_domain_span(sd);
struct cpumask *covered = sched_domains_tmpmask;
struct sd_data *sdd = sd->private;
struct sched_domain *child;
int i;

cpumask_clear(covered);

for_each_cpu(i, span) {
struct cpumask *sg_span;

if (cpumask_test_cpu(i, covered))
continue;

sg = kzalloc_node(sizeof(struct sched_group) + cpumask_size(),
GFP_KERNEL, cpu_to_node(i));

if (!sg)
goto fail;

sg_span = sched_group_cpus(sg);

child = *per_cpu_ptr(sdd->sd, i);
if (child->child) {
child = child->child;
cpumask_copy(sg_span, sched_domain_span(child));
} else
cpumask_set_cpu(i, sg_span);

cpumask_or(covered, covered, sg_span);

sg->sgp = *per_cpu_ptr(sdd->sgp, cpumask_first(sg_span));
atomic_inc(&sg->sgp->ref);

if (cpumask_test_cpu(cpu, sg_span))
groups = sg;

if (!first)
first = sg;
if (last)
last->next = sg;
last = sg;
last->next = first;
}
sd->groups = groups;

return 0;

fail:
free_sched_groups(first, 0);

return -ENOMEM;
}

static int get_group(int cpu, struct sd_data *sdd, struct sched_group **sg)
{
struct sched_domain *sd = *per_cpu_ptr(sdd->sd, cpu);
Expand All @@ -6987,30 +7071,34 @@ static int get_group(int cpu, struct sd_data *sdd, struct sched_group **sg)
if (sg) {
*sg = *per_cpu_ptr(sdd->sg, cpu);
(*sg)->sgp = *per_cpu_ptr(sdd->sgp, cpu);
atomic_set(&(*sg)->sgp->ref, 1); /* for claim_allocations */
}

return cpu;
}

/*
* build_sched_groups takes the cpumask we wish to span, and a pointer
* to a function which identifies what group(along with sched group) a CPU
* belongs to. The return value of group_fn must be a >= 0 and < nr_cpu_ids
* (due to the fact that we keep track of groups covered with a struct cpumask).
*
* build_sched_groups will build a circular linked list of the groups
* covered by the given span, and will set each group's ->cpumask correctly,
* and ->cpu_power to 0.
*
* Assumes the sched_domain tree is fully constructed
*/
static void
build_sched_groups(struct sched_domain *sd)
static int
build_sched_groups(struct sched_domain *sd, int cpu)
{
struct sched_group *first = NULL, *last = NULL;
struct sd_data *sdd = sd->private;
const struct cpumask *span = sched_domain_span(sd);
struct cpumask *covered;
int i;

get_group(cpu, sdd, &sd->groups);
atomic_inc(&sd->groups->ref);

if (cpu != cpumask_first(sched_domain_span(sd)))
return 0;

lockdep_assert_held(&sched_domains_mutex);
covered = sched_domains_tmpmask;

Expand Down Expand Up @@ -7042,6 +7130,8 @@ build_sched_groups(struct sched_domain *sd)
last = sg;
}
last->next = first;

return 0;
}

/*
Expand All @@ -7056,12 +7146,17 @@ build_sched_groups(struct sched_domain *sd)
*/
static void init_sched_groups_power(int cpu, struct sched_domain *sd)
{
WARN_ON(!sd || !sd->groups);
struct sched_group *sg = sd->groups;

if (cpu != group_first_cpu(sd->groups))
return;
WARN_ON(!sd || !sg);

do {
sg->group_weight = cpumask_weight(sched_group_cpus(sg));
sg = sg->next;
} while (sg != sd->groups);

sd->groups->group_weight = cpumask_weight(sched_group_cpus(sd->groups));
if (cpu != group_first_cpu(sg))
return;

update_group_power(sd, cpu);
}
Expand Down Expand Up @@ -7182,16 +7277,15 @@ static enum s_alloc __visit_domain_allocation_hell(struct s_data *d,
static void claim_allocations(int cpu, struct sched_domain *sd)
{
struct sd_data *sdd = sd->private;
struct sched_group *sg = sd->groups;

WARN_ON_ONCE(*per_cpu_ptr(sdd->sd, cpu) != sd);
*per_cpu_ptr(sdd->sd, cpu) = NULL;

if (cpu == cpumask_first(sched_group_cpus(sg))) {
WARN_ON_ONCE(*per_cpu_ptr(sdd->sg, cpu) != sg);
if (atomic_read(&(*per_cpu_ptr(sdd->sg, cpu))->ref))
*per_cpu_ptr(sdd->sg, cpu) = NULL;

if (atomic_read(&(*per_cpu_ptr(sdd->sgp, cpu))->ref))
*per_cpu_ptr(sdd->sgp, cpu) = NULL;
}
}

#ifdef CONFIG_SCHED_SMT
Expand All @@ -7216,7 +7310,7 @@ static struct sched_domain_topology_level default_topology[] = {
#endif
{ sd_init_CPU, cpu_cpu_mask, },
#ifdef CONFIG_NUMA
{ sd_init_NODE, cpu_node_mask, },
{ sd_init_NODE, cpu_node_mask, SDTL_OVERLAP, },
{ sd_init_ALLNODES, cpu_allnodes_mask, },
#endif
{ NULL, },
Expand Down Expand Up @@ -7284,7 +7378,9 @@ static void __sdt_free(const struct cpumask *cpu_map)
struct sd_data *sdd = &tl->data;

for_each_cpu(j, cpu_map) {
kfree(*per_cpu_ptr(sdd->sd, j));
struct sched_domain *sd = *per_cpu_ptr(sdd->sd, j);
if (sd && (sd->flags & SD_OVERLAP))
free_sched_groups(sd->groups, 0);
kfree(*per_cpu_ptr(sdd->sg, j));
kfree(*per_cpu_ptr(sdd->sgp, j));
}
Expand Down Expand Up @@ -7336,8 +7432,11 @@ static int build_sched_domains(const struct cpumask *cpu_map,
struct sched_domain_topology_level *tl;

sd = NULL;
for (tl = sched_domain_topology; tl->init; tl++)
for (tl = sched_domain_topology; tl->init; tl++) {
sd = build_sched_domain(tl, &d, cpu_map, attr, sd, i);
if (tl->flags & SDTL_OVERLAP || sched_feat(FORCE_SD_OVERLAP))
sd->flags |= SD_OVERLAP;
}

while (sd->child)
sd = sd->child;
Expand All @@ -7349,13 +7448,13 @@ static int build_sched_domains(const struct cpumask *cpu_map,
for_each_cpu(i, cpu_map) {
for (sd = *per_cpu_ptr(d.sd, i); sd; sd = sd->parent) {
sd->span_weight = cpumask_weight(sched_domain_span(sd));
get_group(i, sd->private, &sd->groups);
atomic_inc(&sd->groups->ref);

if (i != cpumask_first(sched_domain_span(sd)))
continue;

build_sched_groups(sd);
if (sd->flags & SD_OVERLAP) {
if (build_overlap_sched_groups(sd, i))
goto error;
} else {
if (build_sched_groups(sd, i))
goto error;
}
}
}

Expand Down
2 changes: 2 additions & 0 deletions kernel/sched_features.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -70,3 +70,5 @@ SCHED_FEAT(NONIRQ_POWER, 1)
* using the scheduler IPI. Reduces rq->lock contention/bounces.
*/
SCHED_FEAT(TTWU_QUEUE, 1)

SCHED_FEAT(FORCE_SD_OVERLAP, 0)

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