linux-kernel - Re: [PATCH -mm 1/2] irq_work, Use llist in irq

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Date:	Fri, 02 Sep 2011 09:14:26 +0800
From:	Huang Ying <ying.huang@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: Re: [PATCH -mm 1/2] irq_work, Use llist in irq_work

On 09/01/2011 05:57 PM, Peter Zijlstra wrote:
> On Thu, 2011-09-01 at 16:56 +0800, Huang Ying wrote:
>> Something as follow with llist_empty() seems not work.
>>
>>   empty = llist_empty(irq_work_list);
>>   llist_add(&work->llnode, irq_work_list);
>>   if (empty)
>>           arch_irq_work_raise();
>>
>> Because irq_work IRQ handler or timer IRQ handler may be executed just
>> before "llist_add(&work->llnode, irq_work_list)", so that, although
>> "empty == false", arch_irq_work_raise() still should be executed.
> 
> Right, I was thinking:
> 
> 	llist_add(&work->llist, irq_work_list);
> 	if (llist_empty(&work->llist))
> 		arch_irq_work_raise();
> 
> And then ran into the difference between llist_node and llist_head. Now
> we could sort that by introducing llist_next() and write it like:
> 
> 	if (!llist_next(&work->list))
> 		arch_irq_work_raise();
> 

This reveals some implementation details of llist.  But it will reveal
some implementation details to make llist_add() return whether list is
empty before adding as Mathieu pointed out.  So I think something like
this or just to check work->list->next should be acceptable.

Best Regards,
Huang Ying
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