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

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Message-ID: <20110903173522.GB10744@Krystal>
Date:	Sat, 3 Sep 2011 13:35:22 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:	Huang Ying <ying.huang@...el.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -mm 1/2] irq_work, Use llist in irq_work

* Huang Ying (ying.huang@...el.com) wrote:
> 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.

No. These solutions all appear to have some relatively high level of
ugliness and expose too much of the structure internals.

I'll submit a patch to change the API from llist to llstack shortly for
comments.

Thanks,

Mathieu

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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