[PATCH v3] sched: cpuset: Don't rebuild root domains on suspend-resume

Qais Yousef
2023-02-06T22:14:55Z

Commit f9a25f776d78 ("cpusets: Rebuild root domain deadline accounting information")
enabled rebuilding root domain on cpuset and hotplug operations to
correct deadline accounting.

Rebuilding root domain is a slow operation and we see 10+ of ms delays
on suspend-resume because of that (worst case captures 20ms which
happens often).

Since nothing is expected to change on suspend-resume operation; skip
rebuilding the root domains to regain the some of the time lost.

Achieve this by refactoring the code to pass whether dl accoutning needs
an update to rebuild_sched_domains(). And while at it, rename
rebuild_root_domains() to update_dl_rd_accounting() which I believe is
a more representative name since we are not really rebuilding the root
domains, but rather updating dl accounting at the root domain.

Some users of rebuild_sched_domains() will skip dl accounting update
now:

* Update sched domains when relaxing the domain level in cpuset
which only impacts searching level in load balance
* update sched domains when cpufreq governor changes and we need
to create the perf domains

Users in arch/x86 and arch/s390 are left with the old behavior.

Debugged-by: Rick Yiu <rickyiu@google.com>
Signed-off-by: Qais Yousef (Google) <qyousef@layalina.io>
---

Changes in v3:

* Change the logic to avoid using cpuhp_tasks_frozen which can be racy
and have dependency on context
* Refactor the code to pass whether dl accounting needs to be updated
down the call chain
* Teach cpuset_force_rebuild() to take a reason argument and convert
the variable into int
* Rename rebuild_root_domains() into update_dl_rd_accounting() as
that's what I believe it's only doing

v2 discussion: https://lore.kernel.org/lkml/20230120194822.962958-1-qyousef@layalina.io/
v1 discussion: https://lore.kernel.org/lkml/20221216233501.gh6m75e7s66dmjgo@airbuntu/

arch/s390/kernel/topology.c | 2 +-
arch/x86/kernel/itmt.c | 6 ++---
drivers/base/arch_topology.c | 2 +-
include/linux/cpuset.h | 12 ++++++----
kernel/cgroup/cpuset.c | 43 ++++++++++++++++++++----------------
kernel/sched/core.c | 2 +-
kernel/sched/topology.c | 2 +-
7 files changed, 39 insertions(+), 30 deletions(-)

diff --git a/arch/s390/kernel/topology.c b/arch/s390/kernel/topology.c
index c6eecd4a5302..29d57154a3f1 100644
--- a/arch/s390/kernel/topology.c
+++ b/arch/s390/kernel/topology.c
@@ -333,7 +333,7 @@ int arch_update_cpu_topology(void)

static void topology_work_fn(struct work_struct *work)
{
- rebuild_sched_domains();
+ rebuild_sched_domains(true);
}

void topology_schedule_update(void)
diff --git a/arch/x86/kernel/itmt.c b/arch/x86/kernel/itmt.c
index 9ff480e94511..6f1446223697 100644
--- a/arch/x86/kernel/itmt.c
+++ b/arch/x86/kernel/itmt.c
@@ -56,7 +56,7 @@ static int sched_itmt_update_handler(struct ctl_table *table, int write,

if (!ret && write && old_sysctl != sysctl_sched_itmt_enabled) {
x86_topology_update = true;
- rebuild_sched_domains();
+ rebuild_sched_domains(true);
}

mutex_unlock(&itmt_update_mutex);
@@ -125,7 +125,7 @@ int sched_set_itmt_support(void)
sysctl_sched_itmt_enabled = 1;

x86_topology_update = true;
- rebuild_sched_domains();
+ rebuild_sched_domains(true);

mutex_unlock(&itmt_update_mutex);

@@ -161,7 +161,7 @@ void sched_clear_itmt_support(void)
/* disable sched_itmt if we are no longer ITMT capable */
sysctl_sched_itmt_enabled = 0;
x86_topology_update = true;
- rebuild_sched_domains();
+ rebuild_sched_domains(true);
}

mutex_unlock(&itmt_update_mutex);
diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
index e7d6e6657ffa..90d8a42335e6 100644
--- a/drivers/base/arch_topology.c
+++ b/drivers/base/arch_topology.c
@@ -253,7 +253,7 @@ int topology_update_cpu_topology(void)
static void update_topology_flags_workfn(struct work_struct *work)
{
update_topology = 1;
- rebuild_sched_domains();
+ rebuild_sched_domains(true);
pr_debug("sched_domain hierarchy rebuilt, flags updated\n");
update_topology = 0;
}
diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index d58e0476ee8e..e30d4cd35ef7 100644
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -18,6 +18,10 @@
#include <linux/mmu_context.h>
#include <linux/jump_label.h>

+#define CPUSET_FORCE_REBUILD_RESET 0
+#define CPUSET_FORCE_REBUILD_SUSPEND_RESUME 1
+#define CPUSET_FORCE_REBUILD_PRS_ERROR 2
+
#ifdef CONFIG_CPUSETS

/*
@@ -68,7 +72,7 @@ static inline bool cpusets_insane_config(void)

extern int cpuset_init(void);
extern void cpuset_init_smp(void);
-extern void cpuset_force_rebuild(void);
+extern void cpuset_force_rebuild(int reason);
extern void cpuset_update_active_cpus(void);
extern void cpuset_wait_for_hotplug(void);
extern void cpuset_read_lock(void);
@@ -132,7 +136,7 @@ static inline int cpuset_do_slab_mem_spread(void)

extern bool current_cpuset_is_being_rebound(void);

-extern void rebuild_sched_domains(void);
+extern void rebuild_sched_domains(bool update_dl_accounting);

extern void cpuset_print_current_mems_allowed(void);

@@ -187,7 +191,7 @@ static inline bool cpusets_insane_config(void) { return false; }
static inline int cpuset_init(void) { return 0; }
static inline void cpuset_init_smp(void) {}

-static inline void cpuset_force_rebuild(void) { }
+static inline void cpuset_force_rebuild(int reason) { }

static inline void cpuset_update_active_cpus(void)
{
@@ -276,7 +280,7 @@ static inline bool current_cpuset_is_being_rebound(void)
return false;
}

-static inline void rebuild_sched_domains(void)
+static inline void rebuild_sched_domains(bool update_dl_accounting)
{
partition_sched_domains(1, NULL, NULL);
}
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index a29c0b13706b..e5ddc8e11e5d 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1079,7 +1079,7 @@ static void update_tasks_root_domain(struct cpuset *cs)
css_task_iter_end(&it);
}

-static void rebuild_root_domains(void)
+static void update_dl_rd_accounting(void)
{
struct cpuset *cs = NULL;
struct cgroup_subsys_state *pos_css;
@@ -1117,11 +1117,13 @@ static void rebuild_root_domains(void)

static void
partition_and_rebuild_sched_domains(int ndoms_new, cpumask_var_t doms_new[],
- struct sched_domain_attr *dattr_new)
+ struct sched_domain_attr *dattr_new,
+ bool update_dl_accounting)
{
mutex_lock(&sched_domains_mutex);
partition_sched_domains_locked(ndoms_new, doms_new, dattr_new);
- rebuild_root_domains();
+ if (update_dl_accounting)
+ update_dl_rd_accounting();
mutex_unlock(&sched_domains_mutex);
}

@@ -1136,7 +1138,7 @@ partition_and_rebuild_sched_domains(int ndoms_new, cpumask_var_t doms_new[],
*
* Call with cpuset_rwsem held. Takes cpus_read_lock().
*/
-static void rebuild_sched_domains_locked(void)
+static void rebuild_sched_domains_locked(bool update_dl_accounting)
{
struct cgroup_subsys_state *pos_css;
struct sched_domain_attr *attr;
@@ -1185,19 +1187,19 @@ static void rebuild_sched_domains_locked(void)
ndoms = generate_sched_domains(&doms, &attr);

/* Have scheduler rebuild the domains */
- partition_and_rebuild_sched_domains(ndoms, doms, attr);
+ partition_and_rebuild_sched_domains(ndoms, doms, attr, update_dl_accounting);
}
#else /* !CONFIG_SMP */
-static void rebuild_sched_domains_locked(void)
+static void rebuild_sched_domains_locked(bool update_dl_accounting)
{
}
#endif /* CONFIG_SMP */

-void rebuild_sched_domains(void)
+void rebuild_sched_domains(bool update_dl_accounting)
{
cpus_read_lock();
percpu_down_write(&cpuset_rwsem);
- rebuild_sched_domains_locked();
+ rebuild_sched_domains_locked(update_dl_accounting);
percpu_up_write(&cpuset_rwsem);
cpus_read_unlock();
}
@@ -1681,7 +1683,7 @@ static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp,
rcu_read_unlock();

if (need_rebuild_sched_domains)
- rebuild_sched_domains_locked();
+ rebuild_sched_domains_locked(true);
}

/**
@@ -2136,7 +2138,7 @@ static int update_relax_domain_level(struct cpuset *cs, s64 val)
cs->relax_domain_level = val;
if (!cpumask_empty(cs->cpus_allowed) &&
is_sched_load_balance(cs))
- rebuild_sched_domains_locked();
+ rebuild_sched_domains_locked(false);
}

return 0;
@@ -2202,7 +2204,7 @@ static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs,
spin_unlock_irq(&callback_lock);

if (!cpumask_empty(trialcs->cpus_allowed) && balance_flag_changed)
- rebuild_sched_domains_locked();
+ rebuild_sched_domains_locked(true);

if (spread_flag_changed)
update_tasks_flags(cs);
@@ -2315,7 +2317,7 @@ static int update_prstate(struct cpuset *cs, int new_prs)
update_sibling_cpumasks(parent, cs, &tmpmask);

if (!sched_domain_rebuilt)
- rebuild_sched_domains_locked();
+ rebuild_sched_domains_locked(true);
out:
/*
* Make partition invalid if an error happen
@@ -3389,11 +3391,11 @@ hotplug_update_tasks(struct cpuset *cs,
update_tasks_nodemask(cs);
}

-static bool force_rebuild;
+static int force_rebuild;

-void cpuset_force_rebuild(void)
+void cpuset_force_rebuild(int reason)
{
- force_rebuild = true;
+ force_rebuild = reason;
}

/**
@@ -3489,7 +3491,7 @@ static void cpuset_hotplug_update_tasks(struct cpuset *cs, struct tmpmasks *tmp)
WRITE_ONCE(cs->prs_err, PERR_HOTPLUG);
notify_partition_change(cs, old_prs);
}
- cpuset_force_rebuild();
+ cpuset_force_rebuild(CPUSET_FORCE_REBUILD_PRS_ERROR);
}

/*
@@ -3499,7 +3501,7 @@ static void cpuset_hotplug_update_tasks(struct cpuset *cs, struct tmpmasks *tmp)
else if (is_partition_valid(parent) && is_partition_invalid(cs)) {
update_parent_subparts_cpumask(cs, partcmd_update, NULL, tmp);
if (is_partition_valid(cs))
- cpuset_force_rebuild();
+ cpuset_force_rebuild(CPUSET_FORCE_REBUILD_PRS_ERROR);
}

update_tasks:
@@ -3626,8 +3628,11 @@ static void cpuset_hotplug_workfn(struct work_struct *work)

/* rebuild sched domains if cpus_allowed has changed */
if (cpus_updated || force_rebuild) {
- force_rebuild = false;
- rebuild_sched_domains();
+ bool update_dl_accounting = cpus_updated ||
+ force_rebuild == CPUSET_FORCE_REBUILD_PRS_ERROR;
+
+ force_rebuild = CPUSET_FORCE_REBUILD_RESET;
+ rebuild_sched_domains(update_dl_accounting);
}

free_cpumasks(NULL, ptmp);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 4580fe3e1d0c..d68eac04c851 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -9485,7 +9485,7 @@ static void cpuset_cpu_active(void)
* restore the original sched domains by considering the
* cpuset configurations.
*/
- cpuset_force_rebuild();
+ cpuset_force_rebuild(CPUSET_FORCE_REBUILD_SUSPEND_RESUME);
}
cpuset_update_active_cpus();
}
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index d93c3379e901..bf33b84c511a 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -214,7 +214,7 @@ void rebuild_sched_domains_energy(void)
{
mutex_lock(&sched_energy_mutex);
sched_energy_update = true;
- rebuild_sched_domains();
+ rebuild_sched_domains(false);
sched_energy_update = false;
mutex_unlock(&sched_energy_mutex);
}
--
2.25.1