linux-kernel - Re: [PATCH] workqueue: add __WQ_FREEZING and remove POOL

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Message-ID: <534F193F.2070600@cn.fujitsu.com>
Date:	Thu, 17 Apr 2014 07:58:55 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	Tejun Heo <tj@...nel.org>
CC:	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] workqueue: add __WQ_FREEZING and remove POOL_FREEZING

On 04/17/2014 03:51 AM, Tejun Heo wrote:
> Hello,
> 
> On Tue, Mar 25, 2014 at 05:56:04PM +0800, Lai Jiangshan wrote:
>> freezing is nothing related to pools, but POOL_FREEZING adds a connection,
>> and causes freeze_workqueues_begin() and thaw_workqueues() complicated.
>>
>> Since freezing is workqueue instance attribute, so we introduce __WQ_FREEZING
>> to wq->flags instead and remove POOL_FREEZING.
>>
>> we set __WQ_FREEZING only when freezable(to simplify pwq_adjust_max_active()),
>> make freeze_workqueues_begin() and thaw_workqueues() fast skip non-freezable wq.
> 
> Please wrap the description to 80 columns.
> 
>> @@ -3730,18 +3726,13 @@ static void pwq_unbound_release_workfn(struct work_struct *work)
>>  static void pwq_adjust_max_active(struct pool_workqueue *pwq)
>>  {
>>  	struct workqueue_struct *wq = pwq->wq;
>> -	bool freezable = wq->flags & WQ_FREEZABLE;
>>  
>> -	/* for @wq->saved_max_active */
>> +	/* for @wq->saved_max_active and @wq->flags */
>>  	lockdep_assert_held(&wq->mutex);
>>  
>> -	/* fast exit for non-freezable wqs */
>> -	if (!freezable && pwq->max_active == wq->saved_max_active)
>> -		return;
>> -
> 
> Why are we removing the above?  Can't we still test __WQ_FREEZING as
> we're holding wq->mutex?  I don't really mind removing the
> optimization but the patch description at least has to explain what's
> going on.

This part was in other old patch: https://lkml.org/lkml/2013/4/3/756
I admit the changelogs(old patch&this) are bad.
But I still consider it would be better if we split it to two patches:
(https://lkml.org/lkml/2013/4/3/748 & https://lkml.org/lkml/2013/4/3/756)

There are different aims in the patches.

Any thinks? And sorry for I didn't keep to push the patches at that time.
Thanks
Lai

> 
> ...
>>  	list_for_each_entry(wq, &workqueues, list) {
>> +		if (!(wq->flags & WQ_FREEZABLE))
>> +			continue;
> 
> Ah, okay, you're not calling the function at all if WQ_FREEZABLE is
> not set.  I couldn't really understand what you were trying to say in
> the patch description.  Can you please try to refine the description
> more?  It's better to be verbose and clear than short and difficult to
> understand.
> 
> Thanks.
> 

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