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Date: Wed, 18 Nov 2020 17:05:20 +0800
From: Yunfeng Ye <yeyunfeng@...wei.com>
To: Lai Jiangshan <jiangshanlai@...il.com>
CC: Tejun Heo <tj@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
Shiyuan Hu <hushiyuan@...wei.com>,
Hewenliang <hewenliang4@...wei.com>
Subject: Re: workqueue: Only kick a worker after thawed or for an unbound
workqueue
On 2020/11/18 14:26, Yunfeng Ye wrote:
>
>
> On 2020/11/18 12:06, Lai Jiangshan wrote:
>> On Tue, Nov 17, 2020 at 3:33 PM Yunfeng Ye <yeyunfeng@...wei.com> wrote:
>>>
>>> In realtime scenario, We do not want to have interference on the
>>> isolated cpu cores. but when invoking alloc_workqueue() for percpu wq
>>> on the housekeeping cpu, it kick a kworker on the isolated cpu.
>>>
>>> alloc_workqueue
>>> pwq_adjust_max_active
>>> wake_up_worker
>>>
>>> The comment in pwq_adjust_max_active() said:
>>> "Need to kick a worker after thawed or an unbound wq's
>>> max_active is bumped"
>>>
>>> So it is unnecessary to kick a kworker for percpu wq's when
>>> alloc_workqueue. this patch only kick a worker after thawed or for an
>>> unbound workqueue.
>>>
>>> Signed-off-by: Yunfeng Ye <yeyunfeng@...wei.com>
>>> ---
>>> kernel/workqueue.c | 18 +++++++++++++-----
>>> 1 file changed, 13 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
>>> index c41c3c17b86a..80f7bbd4889f 100644
>>> --- a/kernel/workqueue.c
>>> +++ b/kernel/workqueue.c
>>> @@ -3696,14 +3696,16 @@ static void pwq_unbound_release_workfn(struct work_struct *work)
>>> }
>>>
>>> /**
>>> - * pwq_adjust_max_active - update a pwq's max_active to the current setting
>>> + * pwq_adjust_max_active_and_kick - update a pwq's max_active to the current setting
>>> * @pwq: target pool_workqueue
>>> + * @force_kick: force to kick a worker
>>> *
>>> * If @pwq isn't freezing, set @pwq->max_active to the associated
>>> * workqueue's saved_max_active and activate delayed work items
>>> * accordingly. If @pwq is freezing, clear @pwq->max_active to zero.
>>> */
>>> -static void pwq_adjust_max_active(struct pool_workqueue *pwq)
>>> +static void pwq_adjust_max_active_and_kick(struct pool_workqueue *pwq,
>>> + bool force_kick)
>>> {
>>> struct workqueue_struct *wq = pwq->wq;
>>> bool freezable = wq->flags & WQ_FREEZABLE;
>>> @@ -3733,9 +3735,10 @@ static void pwq_adjust_max_active(struct pool_workqueue *pwq)
>>>
>>> /*
>>> * Need to kick a worker after thawed or an unbound wq's
>>> - * max_active is bumped. It's a slow path. Do it always.
>>> + * max_active is bumped.
>>
>>
>> Hello
>>
>> Thanks for reporting the problem.
>>
>> But I don't like to add an argument. The waking up is called
>> always just because it was considered no harm and it is slow
>> path. But it can still be possible to detect if the waking up
>> is really needed based on the actual activation of delayed works.
>>
>> The previous lines are:
>>
>> while (!list_empty(&pwq->delayed_works) &&
>> pwq->nr_active < pwq->max_active)
>> pwq_activate_first_delayed(pwq);
>>
>> And you can record the old pwq->nr_active before these lines:
>>
>> int old_nr_active = pwq->nr_active;
>>
>> while (!list_empty(&pwq->delayed_works) &&
>> pwq->nr_active < pwq->max_active)
>> pwq_activate_first_delayed(pwq);
>>
>> /* please add more comments here, see 951a078a5 */
>> if (old_nr_active < pwq->nr_active) {
>> if (!old_nr_active || (wq->flags & WQ_UNBOUND))
>> wake_up_worker(pwq->pool);
>> }
>>
> Ok, I will send a patch v2.
> Thanks.
>
I think it is unnecessary to distinguish the percpu or unbound's wq,
kick a worker always based on the actual activation of delayed works.
Look like this:
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index c41c3c17b86a..cd551dcb2cc9 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -3725,17 +3725,23 @@ static void pwq_adjust_max_active(struct pool_workqueue *pwq)
* is updated and visible.
*/
if (!freezable || !workqueue_freezing) {
+ bool kick = false;
+
pwq->max_active = wq->saved_max_active;
while (!list_empty(&pwq->delayed_works) &&
- pwq->nr_active < pwq->max_active)
+ pwq->nr_active < pwq->max_active) {
pwq_activate_first_delayed(pwq);
+ kick = true;
+ }
/*
* Need to kick a worker after thawed or an unbound wq's
- * max_active is bumped. It's a slow path. Do it always.
+ * max_active is bumped. It's a slow path. Do it always
+ * based on the actual activation of delayed works.
*/
- wake_up_worker(pwq->pool);
+ if (kick)
+ wake_up_worker(pwq->pool);
} else {
pwq->max_active = 0;
}
Is it OK?
Thanks.
>>
>> Thanks for your work.
>> Lai.
>>
>>> */
>>> - wake_up_worker(pwq->pool);
>>> + if (force_kick || (wq->flags & WQ_UNBOUND))
>>> + wake_up_worker(pwq->pool);
>>> } else {
>>> pwq->max_active = 0;
>>> }
>>> @@ -3743,6 +3746,11 @@ static void pwq_adjust_max_active(struct pool_workqueue *pwq)
>>> raw_spin_unlock_irqrestore(&pwq->pool->lock, flags);
>>> }
>>>
>>> +static void pwq_adjust_max_active(struct pool_workqueue *pwq)
>>> +{
>>> + pwq_adjust_max_active_and_kick(pwq, false);
>>> +}
>>> +
>>> /* initialize newly alloced @pwq which is associated with @wq and @pool */
>>> static void init_pwq(struct pool_workqueue *pwq, struct workqueue_struct *wq,
>>> struct worker_pool *pool)
>>> @@ -5252,7 +5260,7 @@ void thaw_workqueues(void)
>>> list_for_each_entry(wq, &workqueues, list) {
>>> mutex_lock(&wq->mutex);
>>> for_each_pwq(pwq, wq)
>>> - pwq_adjust_max_active(pwq);
>>> + pwq_adjust_max_active_and_kick(pwq, true);
>>> mutex_unlock(&wq->mutex);
>>> }
>>>
>>> --
>>> 2.18.4
>> .
>>
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