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Subject: Re: [RFC PATCH 1/6] kernel: implement queue spinlock API
From: Eric Dumazet <eric.dumazet@gmail.com>
To: Michel Lespinasse <walken@google.com>
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Date: Thu, 07 Feb 2013 16:03:54 -0800
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On Thu, 2013-02-07 at 15:58 -0800, Michel Lespinasse wrote:

> No, I think that's doable. The trick would be that once a thread
> acquires the lock, the only remaining use of the node is to receive
> the 'next' pointer if/when another thread starts contending for the
> lock. So if the lock state would need to distinguish between a lock
> that is currently locked but not contended (the next value would then
> be NULL), and a lock that is currently locked and contended (the
> lock->next value is the node that goes after the current lock owner)
> 

It adds yet another memory write to store the node pointer in the
lock...

I suspect it's going to increase false sharing.