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Message-ID: <50c66213-87c5-71c9-7dc5-1653a1bacc50@huawei.com>
Date: Thu, 19 Nov 2020 10:25:57 +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 2020/11/19 9:58, Lai Jiangshan wrote:
> On Wed, Nov 18, 2020 at 5:05 PM Yunfeng Ye <yeyunfeng@...wei.com> wrote:
>>
>>
>>
>> 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.
>
>
> It is OK, since it is a slow path. Please also add
> comments to the code for reasons not to wake up in
> some cases as described in your previous comments.
>
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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