linux-kernel - Re: poll: allow f_op->poll to sleep, take #3

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Date:	Sun, 23 Nov 2008 18:14:46 +0900
From:	Tejun Heo <htejun@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Davide Libenzi <davidel@...ilserver.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Matthew Wilcox <matthew@....cx>,
	Miklos Szeredi <miklos@...redi.hu>, arjan@...ux.intel.com,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	hch@...radead.org, rminnich@...dia.gov, ericvh@...il.com,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org
Subject: Re: poll: allow f_op->poll to sleep, take #3

Ingo Molnar wrote:
> * Davide Libenzi <davidel@...ilserver.org> wrote:
> 
>> On Sun, 23 Nov 2008, Tejun Heo wrote:
>>
>>> +static int pollwake(wait_queue_t *wait, unsigned mode, int sync, void *key)
>>> +{
>>> +	struct poll_wqueues *pwq = wait->private;
>>> +	DECLARE_WAITQUEUE(dummy_wait, pwq->polling_task);
>>> +
>>> +	set_mb(pwq->triggered, 1);
>>> +
>>> +	/* perform the default wake up operation */
>>> +	return default_wake_function(&dummy_wait, mode, sync, key);
>>> +}
>> Wouldn't it be nicer to un-static try_to_wake_up() (or a wrapper) 
>> instead of setting up a fake wait queue just to use 
>> default_wake_function(), just to wake up a task?
> 
> the already existing single-task-wakeup shortcut method made available 
> by the scheduler is wake_up_process(). A number of primitives where 
> waitqueue overhead is of concern already make use of it. 
> (mutexes/rtmutexes and more)
> 
> if you need a different mode flag, then please extend the 
> wake_up_process() family of APIs.

Well, the problem is that for wait wake up functions @mode and @sync are
passed as parameter and should be passed over to actual wake up function
as-is, if I add @mode and @sync to wake_up_process() family of APIs,
it's just try_to_wake_up().

Thanks.

-- 
tejun
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