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Subject[PATCH 28/35] workqueue: increase max_active of keventd and kill current_is_keventd()
Date
Define WQ_MAX_ACTIVE and create keventd with max_active set to half of
it which means that keventd now can process upto WQ_MAX_ACTIVE / 2 - 1
works concurrently. Unless some combination can result in dependency
loop longer than max_active, deadlock won't happen and thus it's
unnecessary to check whether current_is_keventd() before trying to
schedule a work. Kill current_is_keventd().

(Lockdep annotations are broken. We need lock_map_acquire_read_norecurse())

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Oleg Nesterov <oleg@redhat.com>
---
arch/ia64/kernel/smpboot.c | 2 +-
arch/x86/kernel/smpboot.c | 2 +-
include/linux/workqueue.h | 4 ++-
kernel/workqueue.c | 63 +++++++++----------------------------------
4 files changed, 18 insertions(+), 53 deletions(-)

diff --git a/arch/ia64/kernel/smpboot.c b/arch/ia64/kernel/smpboot.c
index 6a1380e..99dcc85 100644
--- a/arch/ia64/kernel/smpboot.c
+++ b/arch/ia64/kernel/smpboot.c
@@ -519,7 +519,7 @@ do_boot_cpu (int sapicid, int cpu)
/*
* We can't use kernel_thread since we must avoid to reschedule the child.
*/
- if (!keventd_up() || current_is_keventd())
+ if (!keventd_up())
c_idle.work.func(&c_idle.work);
else {
schedule_work(&c_idle.work);
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index c4f33b2..4d90f37 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -735,7 +735,7 @@ static int __cpuinit do_boot_cpu(int apicid, int cpu)
goto do_rest;
}

- if (!keventd_up() || current_is_keventd())
+ if (!keventd_up())
c_idle.work.func(&c_idle.work);
else {
schedule_work(&c_idle.work);
diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index b8f4ec4..33e24e7 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -227,6 +227,9 @@ enum {
WQ_SINGLE_CPU = 1 << 1, /* only single cpu at a time */
WQ_NON_REENTRANT = 1 << 2, /* guarantee non-reentrance */
WQ_RESCUER = 1 << 3, /* has an rescue worker */
+
+ WQ_MAX_ACTIVE = 512, /* I like 512, better ideas? */
+ WQ_DFL_ACTIVE = WQ_MAX_ACTIVE / 2,
};

extern struct workqueue_struct *
@@ -280,7 +283,6 @@ extern int schedule_delayed_work(struct delayed_work *work, unsigned long delay)
extern int schedule_delayed_work_on(int cpu, struct delayed_work *work,
unsigned long delay);
extern int schedule_on_each_cpu(work_func_t func);
-extern int current_is_keventd(void);
extern int keventd_up(void);

extern void init_workqueues(void);
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 09e9677..a5a36f3 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -2398,7 +2398,6 @@ EXPORT_SYMBOL(schedule_delayed_work_on);
int schedule_on_each_cpu(work_func_t func)
{
int cpu;
- int orig = -1;
struct work_struct *works;

works = alloc_percpu(struct work_struct);
@@ -2407,23 +2406,12 @@ int schedule_on_each_cpu(work_func_t func)

get_online_cpus();

- /*
- * When running in keventd don't schedule a work item on
- * itself. Can just call directly because the work queue is
- * already bound. This also is faster.
- */
- if (current_is_keventd())
- orig = raw_smp_processor_id();
-
for_each_online_cpu(cpu) {
struct work_struct *work = per_cpu_ptr(works, cpu);

INIT_WORK(work, func);
- if (cpu != orig)
- schedule_work_on(cpu, work);
+ schedule_work_on(cpu, work);
}
- if (orig >= 0)
- func(per_cpu_ptr(works, orig));

for_each_online_cpu(cpu)
flush_work(per_cpu_ptr(works, cpu));
@@ -2494,41 +2482,6 @@ int keventd_up(void)
return keventd_wq != NULL;
}

-int current_is_keventd(void)
-{
- bool found = false;
- unsigned int cpu;
-
- /*
- * There no longer is one-to-one relation between worker and
- * work queue and a worker task might be unbound from its cpu
- * if the cpu was offlined. Match all busy workers. This
- * function will go away once dynamic pool is implemented.
- */
- for_each_possible_cpu(cpu) {
- struct global_cwq *gcwq = get_gcwq(cpu);
- struct worker *worker;
- struct hlist_node *pos;
- unsigned long flags;
- int i;
-
- spin_lock_irqsave(&gcwq->lock, flags);
-
- for_each_busy_worker(worker, i, pos, gcwq) {
- if (worker->task == current) {
- found = true;
- break;
- }
- }
-
- spin_unlock_irqrestore(&gcwq->lock, flags);
- if (found)
- break;
- }
-
- return found;
-}
-
static struct cpu_workqueue_struct *alloc_cwqs(void)
{
const size_t size = sizeof(struct cpu_workqueue_struct);
@@ -2570,6 +2523,16 @@ static void free_cwqs(struct cpu_workqueue_struct *cwqs)
#endif
}

+static int wq_clamp_max_active(int max_active, const char *name)
+{
+ if (max_active < 1 || max_active > WQ_MAX_ACTIVE)
+ printk(KERN_WARNING "workqueue: max_active %d requested for %s "
+ "is out of range, clamping between %d and %d\n",
+ max_active, name, 1, WQ_MAX_ACTIVE);
+
+ return clamp_val(max_active, 1, WQ_MAX_ACTIVE);
+}
+
struct workqueue_struct *__create_workqueue_key(const char *name,
unsigned int flags,
int max_active,
@@ -2579,7 +2542,7 @@ struct workqueue_struct *__create_workqueue_key(const char *name,
struct workqueue_struct *wq;
unsigned int cpu;

- max_active = clamp_val(max_active, 1, INT_MAX);
+ max_active = wq_clamp_max_active(max_active, name);

wq = kzalloc(sizeof(*wq), GFP_KERNEL);
if (!wq)
@@ -3326,6 +3289,6 @@ void __init init_workqueues(void)
spin_unlock_irq(&gcwq->lock);
}

- keventd_wq = create_workqueue("events");
+ keventd_wq = __create_workqueue("events", 0, WQ_DFL_ACTIVE);
BUG_ON(!keventd_wq);
}
--
1.6.4.2


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