From: Daniel Wagner <daniel.wagner@xxxxxxxxxxxx>
Hi,
As Peter correctly pointed out in [1] a simple conversion from
wait to swait in completion.c wont work. I played a bit around and
came up with this rather ugly idea.
So in case complete_all() is called in hard irq context we just wake
up one waiter and let that one call swake_up_all(). For this I needed
to somehow transfer this information from complete_all() to
wait_for_completion(). The only working idea I found was to introduce
a new flag in struct completion. Ideas to overcome this problem
are highly appreciated.
I did also some performance measurement with below test program. The
test creates a trigger thread and a bunch of waiter threads. The
trigger thread calls complete_all() either from thread context or from
hard irq context. Time needed for 1000 iterations measured. This was
done on a idle IvyBridge machine with 64 logial cores (E5-4610).
waiter_nr: number of waiter threads
irqwork: 0 complete_all() from thread context, 1 complete_all() from irq_work()
wait:
waiter_nr 64
irqwork 0
count 66.000000
mean 0.378318
std 0.018468
min 0.344000
25% 0.364000
50% 0.382500
75% 0.395000
max 0.407000
swait:
waiter_nr 64
irqwork 1
count 86.000000
mean 0.315221
std 0.007115
min 0.291000
25% 0.312000
50% 0.316500
75% 0.320000
max 0.329000
swait:
waiter_nr 64
irqwork 0
count 81.000000
mean 0.344642
std 0.021708
min 0.294000
25% 0.336000
50% 0.341000
75% 0.355000
max 0.403000
cheers,
daniel
completion-test.c:
#include <linux/module.h>
#include <linux/wait.h>
#include <linux/swait.h>
#include <linux/kthread.h>
#include <linux/threads.h>
#include <linux/slab.h>
#include <linux/delay.h>
#include <linux/completion.h>
#include <linux/irq_work.h>
static unsigned int waiter_nr = 5;
static bool irqwork = true;
static unsigned int counter = 1000;
module_param(waiter_nr, uint,
S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP);
MODULE_PARM_DESC(waiter_nr, "Number of waiter threads");
module_param(irqwork, bool,
S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP);
MODULE_PARM_DESC(irqwork, "irqwork");
module_param(counter, uint,
S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP);
MODULE_PARM_DESC(counter, "counter");
struct completion_test {
/* We need two completions to avoid a race with reinit of the
* completion.
*/
struct completion sync_stage1;
struct completion sync_stage2;
wait_queue_head_t wq_stage1;
wait_queue_head_t wq_stage2;
atomic_t cnt_stage1;
atomic_t cnt_stage2;
struct irq_work irq_work;
};
static struct completion_test test_data;
static struct task_struct **waiter_tasks;
static struct task_struct *trigger_task;
static void trigger_irq(struct irq_work *arg)
{
struct completion_test *ct =
container_of(arg, struct completion_test, irq_work);
complete_all(&ct->sync_stage1);
}
static int waiter(void *arg)
{
struct completion_test *ct = arg;
for (;;) {
atomic_inc(&ct->cnt_stage1);
wake_up(&ct->wq_stage1);
wait_for_completion_interruptible(&ct->sync_stage1);
if (kthread_should_stop())
break;
atomic_inc(&ct->cnt_stage2);
wake_up(&ct->wq_stage2);
wait_for_completion_interruptible(&ct->sync_stage2);
if (kthread_should_stop())
break;
}
return 0;
}
static int trigger(void *arg)
{
struct completion_test *ct = arg;
struct timespec ts_start, ts;
unsigned long cnt;
cnt = counter;
ts_start = current_kernel_time();
for (;;) {
cnt--;
if (cnt == 0) {
ts = timespec_sub(current_kernel_time(), ts_start);
printk("%ld.%.9ld\n", ts.tv_sec, ts.tv_nsec);
cnt = counter;
ts_start = current_kernel_time();
}
wait_event_interruptible(ct->wq_stage1,
!(atomic_read(&ct->cnt_stage1) < waiter_nr));
if (kthread_should_stop()) {
complete_all(&ct->sync_stage1);
break;
}
atomic_set(&ct->cnt_stage2, 0);
reinit_completion(&ct->sync_stage2);
if (irqwork)
irq_work_queue(&ct->irq_work);
else
complete_all(&ct->sync_stage1);
wait_event_interruptible(ct->wq_stage2,
!(atomic_read(&ct->cnt_stage2) < waiter_nr));
if (kthread_should_stop()) {
complete_all(&ct->sync_stage2);
break;
}
reinit_completion(&ct->sync_stage1);
atomic_set(&ct->cnt_stage1, 0);
complete_all(&ct->sync_stage2);
}
return 0;
}
static void __exit completion_test_module_cleanup(void)
{
unsigned int i;
if (trigger_task)
kthread_stop(trigger_task);
if (waiter_tasks) {
for (i = 0; i < waiter_nr; i++) {
if (waiter_tasks[i] && !IS_ERR(waiter_tasks[i]))
kthread_stop(waiter_tasks[i]);
}
kfree(waiter_tasks);
}
}
static int __init completion_test_module_init(void)
{
struct completion_test *ct = &test_data;
unsigned int i;
int err;
init_completion(&ct->sync_stage1);
init_completion(&ct->sync_stage2);
init_waitqueue_head(&ct->wq_stage1);
init_waitqueue_head(&ct->wq_stage2);
atomic_set(&ct->cnt_stage1, 0);
atomic_set(&ct->cnt_stage2, 0);
init_irq_work(&ct->irq_work, trigger_irq);
waiter_tasks = kcalloc(waiter_nr, sizeof(waiter_tasks[0]), GFP_KERNEL);
if (!waiter_tasks) {
printk("out of memory\n");
err = -ENOMEM;
goto unwind;
}
for (i = 0; i < waiter_nr; i++) {
waiter_tasks[i] = kthread_run(waiter, ct, "waiter");
if (IS_ERR(waiter_tasks[i])) {
err = -PTR_ERR(waiter_tasks[i]);
goto unwind;
}
}
trigger_task = kthread_run(trigger, ct, "trigger");
if (IS_ERR(trigger_task)) {
err = -PTR_ERR(trigger_task);
goto unwind;
}
return 0;
unwind:
completion_test_module_cleanup();
return err;
}
module_init(completion_test_module_init);
module_exit(completion_test_module_cleanup);
MODULE_LICENSE("GPL v2");
MODULE_AUTHOR("Daniel Wagner");
MODULE_DESCRIPTION("completion test");
[1] http://thread.gmane.org/gmane.linux.kernel/2034867/focus=2034873
Daniel Wagner (1):
sched/completion: convert completions to use simple wait queues
include/linux/completion.h | 14 ++++++++++----
kernel/sched/completion.c | 41 +++++++++++++++++++++++++----------------
2 files changed, 35 insertions(+), 20 deletions(-)
--
2.5.0
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