linux-kernel - Re: [RFC PATCH 1/6] kernel: implement queue spinlock API

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Date:	Thu, 07 Feb 2013 15:14:05 -0800
From:	John Stultz <john.stultz@...aro.org>
To:	paulmck@...ux.vnet.ibm.com
CC:	Michel Lespinasse <walken@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	Ingo Molnar <mingo@...hat.com>,
	David Howells <dhowells@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Eric Dumazet <edumazet@...gle.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Manfred Spraul <manfred@...orfullife.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/6] kernel: implement queue spinlock API

On 02/07/2013 02:34 PM, Paul E. McKenney wrote:
> On Tue, Jan 22, 2013 at 03:13:30PM -0800, Michel Lespinasse wrote:
>> Introduce queue spinlocks, to be used in situations where it is desired
>> to have good throughput even under the occasional high-contention situation.
>>
>> This initial implementation is based on the classic MCS spinlock,
>> because I think this represents the nicest API we can hope for in a
>> fast queue spinlock algorithm. The MCS spinlock has known limitations
>> in that it performs very well under high contention, but is not as
>> good as the ticket spinlock under low contention. I will address these
>> limitations in a later patch, which will propose an alternative,
>> higher performance implementation using (mostly) the same API.
>>
>> Sample use case acquiring mystruct->lock:
>>
>>    struct q_spinlock_node node;
>>
>>    q_spin_lock(&mystruct->lock, &node);
>>    ...
>>    q_spin_unlock(&mystruct->lock, &node);
> It is possible to keep the normal API for MCS locks by having the lock
> holder remember the parameter in the lock word itself.  While spinning,
> the node is on the stack, is not needed once the lock is acquired.
> The pointer to the next node in the queue -is- needed, but this can be
> stored in the lock word.
>
> I believe that John Stultz worked on something like this some years back,
> so added him to CC.
Oh yea, its been quite awhile.

Here are some of the discussion threads google remembers for me:

http://marc.info/?l=lse-tech&m=101227079817027&w=2

http://marc.info/?l=lse-tech&m=101380783015065&w=2  (missing the patch)
     http://marc.info/?l=lse-tech&m=101380783615084&w=2 (patch for above)


thanks
-john


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