Hi Tejun & Peter,
Could you please share your feedback on this patch for making
cpuset_hotplug_workfn synchronous.
Thanks,
Prateek
On 1/24/2020 8:37 PM, Prateek Sood wrote:
Hi Tejun & Peter,
It seems that after following patch we can make cpuset_hotplug_workfn
synchronous:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/kernel/cgroup/cpuset.c?h=v5.5-rc7&id=d74b27d63a8bebe2fe634944e4ebdc7b10db7a39
Could you please share your opinion on the same and below patch.
Thanks,
Prateek
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Convert cpuset_hotplug_workfn() into synchronous call for cpu hotplug
path. For memory hotplug path it still gets queued as a work item.
Since cpuset_hotplug_workfn() can be made synchronous for cpu hotplug
path, it is not required to wait for cpuset hotplug while thawing
processes.
Signed-off-by: Prateek Sood <prsood@xxxxxxxxxxxxxx>
---
include/linux/cpuset.h | 3 ---
kernel/cgroup/cpuset.c | 31 +++++++++++++++++++------------
kernel/power/process.c | 2 --
3 files changed, 19 insertions(+), 17 deletions(-)
diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index 04c20de66..cede4cb 100644
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -54,7 +54,6 @@ static inline void cpuset_dec(void)
extern void cpuset_init_smp(void);
extern void cpuset_force_rebuild(void);
extern void cpuset_update_active_cpus(void);
-extern void cpuset_wait_for_hotplug(void);
extern void cpuset_read_lock(void);
extern void cpuset_read_unlock(void);
extern void cpuset_cpus_allowed(struct task_struct *p, struct cpumask *mask);
@@ -176,8 +175,6 @@ static inline void cpuset_update_active_cpus(void)
partition_sched_domains(1, NULL, NULL);
}
-static inline void cpuset_wait_for_hotplug(void) { }
-
static inline void cpuset_read_lock(void) { }
static inline void cpuset_read_unlock(void) { }
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 58f5073..cafd4d2 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -3101,7 +3101,7 @@ static void cpuset_hotplug_update_tasks(struct cpuset *cs, struct tmpmasks *tmp)
}
/**
- * cpuset_hotplug_workfn - handle CPU/memory hotunplug for a cpuset
+ * cpuset_hotplug - handle CPU/memory hotunplug for a cpuset
*
* This function is called after either CPU or memory configuration has
* changed and updates cpuset accordingly. The top_cpuset is always
@@ -3116,7 +3116,7 @@ static void cpuset_hotplug_update_tasks(struct cpuset *cs, struct tmpmasks *tmp)
* Note that CPU offlining during suspend is ignored. We don't modify
* cpusets across suspend/resume cycles at all.
*/
-static void cpuset_hotplug_workfn(struct work_struct *work)
+static void cpuset_hotplug(bool use_cpu_hp_lock)
{
static cpumask_t new_cpus;
static nodemask_t new_mems;
@@ -3201,25 +3201,32 @@ 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();
+ if (use_cpu_hp_lock)
+ rebuild_sched_domains();
+ else {
+ /* Acquiring cpu_hotplug_lock is not required.
+ * When cpuset_hotplug() is called in hotplug path,
+ * cpu_hotplug_lock is held by the hotplug context
+ * which is waiting for cpuhp_thread_fun to indicate
+ * completion of callback.
+ */
+ percpu_down_write(&cpuset_rwsem);
+ rebuild_sched_domains_locked();
+ percpu_up_write(&cpuset_rwsem);
+ }
}
free_cpumasks(NULL, ptmp);
}
-void cpuset_update_active_cpus(void)
+static void cpuset_hotplug_workfn(struct work_struct *work)
{
- /*
- * We're inside cpu hotplug critical region which usually nests
- * inside cgroup synchronization. Bounce actual hotplug processing
- * to a work item to avoid reverse locking order.
- */
- schedule_work(&cpuset_hotplug_work);
+ cpuset_hotplug(true);
}
-void cpuset_wait_for_hotplug(void)
+void cpuset_update_active_cpus(void)
{
- flush_work(&cpuset_hotplug_work);
+ cpuset_hotplug(false);
}
/*
diff --git a/kernel/power/process.c b/kernel/power/process.c
index 4b6a54d..08f7019 100644
--- a/kernel/power/process.c
+++ b/kernel/power/process.c
@@ -204,8 +204,6 @@ void thaw_processes(void)
__usermodehelper_set_disable_depth(UMH_FREEZING);
thaw_workqueues();
- cpuset_wait_for_hotplug();
-
read_lock(&tasklist_lock);
for_each_process_thread(g, p) {
/* No other threads should have PF_SUSPEND_TASK set */
--
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