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

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Message-ID: <1314871201.7945.17.camel@twins>
Date:	Thu, 01 Sep 2011 12:00:01 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Huang Ying <ying.huang@...el.com>
Cc:	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

On Thu, 2011-09-01 at 16:44 +0800, Huang Ying wrote:

> Because llist is in library, it may be used in highly contended case and
> light/un-contended loads.  So maybe code as above is best choice for llist.

Well the thing is, if you're heavily contended you should probably be
doing something else..

> > Also, just noticed, why do you have different list_head/list_node
> > structures? They're the same, a single pointer.
> 
> There is only one structure before (llist_head).  Linus give me some
> comments about that, suggests to use 2 structures.  I think his comments
> are reasonable.  Copied here:

OK

> Even with this_cpu_* ops, it seems that the race condition I described
> is still possible.
> 
> - use this_cpu_cmpxchg to queue irq_work into irq_work_list of CPU A
> - preempted and resumed execution on CPU B
> - arch_irq_work_raise on CPU B
> 
> Do you think so?

No you're right, got my brain inside-out today or so..
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