linux-kernel - Re: [PATCH -v10 0/4] Lock-less list

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Date:	Thu, 20 Jan 2011 16:57:06 +0800
From:	huang ying <huang.ying.caritas@...il.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:	Huang Ying <ying.huang@...el.com>, linux-kernel@...r.kernel.org,
	Andi Kleen <andi@...stfloor.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Chris Mason <chris.mason@...cle.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH -v10 0/4] Lock-less list

Hi, Mathieu,

On Thu, Jan 20, 2011 at 1:55 PM, Mathieu Desnoyers
<mathieu.desnoyers@...icios.com> wrote:
> Hi Huang,
>
> I just found out about your lockless linked-list implementation, it looks
> interesting. Paul McKenney and myself have created a similar implementation for
> userspace within the Userspace RCU project, you might want to have a look (it's
> LGPLv2.1).
>
> One point about semantic: a singly-linked list for which you can either delete
> the first element or all the elements should probably be called a stack ? I'm
> therefore going to refer to "push/pop" in this email rather than "add/delete".
>
> We've got two linked-list stack implementations in the userspace RCU tree:
>
> One has wait-free push, and blocking pop. Useful if you can afford to block when
> you pop from the list. There is no restriction on the number of concurrent
> push/pop to/from the list. The code is at:
>
> http://git.lttng.org/?p=userspace-rcu.git;a=blob;f=urcu/wfstack-static.h
>
> The other has lock-free push and pop, no restriction on the number of concurrent
> push/pop, but uses a clever trick that ensures that the cmpxchg loop will never
> see a re-used pointer by using a RCU read-side to protect from memory reclaim.
> It therefore requires that the memory used for the list must only be freed after
> a RCU grace period. The code is at:
>
> http://git.lttng.org/?p=userspace-rcu.git;a=blob;f=urcu/rculfstack-static.h
>
> We could probably extend this to allow popping all stack entries in one go, but
> I haven't given it much thought.
>
> We also have queue implementations (enqueue at head, dequeue at tail). The first
> has wait-free enqueue/blocking dequeue and the second has lock-free
> enqueue/dequeue. We use the wait-free enqueue/blocking dequeue queue to push
> RCU callbacks when call_rcu() is executed from real-time threads, and we then
> dequeue the callbacks to execute with a blocking thread. The lock-free
> enqueue/dequeue queue also needs a reference count on the "dummy" node it keeps
> in addition to use RCU to delay memory reclamation (see comments in the code).
>
> wait-free enqueue/blocking dequeue:
>
> http://git.lttng.org/?p=userspace-rcu.git;a=blob;f=urcu/wfqueue-static.h
>
> lock-free enqueue/dequeue (beware, the refcounting makes the API less elegant
> than the other implementations):
>
> http://git.lttng.org/?p=userspace-rcu.git;a=blob;f=urcu/rculfqueue-static.h
>
> Hoping this might be helpful to you,

Thanks!  I will investigate your code!

Best Regards,
Huang Ying
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