Re: [PATCH v2] ipc/msg: Implement lockless pipelined wakeups

From: Davidlohr Bueso
Date: Wed Nov 04 2015 - 12:32:32 EST

On Wed, 04 Nov 2015, Peter Zijlstra wrote:

On Tue, Nov 03, 2015 at 04:03:29PM +0100, Sebastian Andrzej Siewior wrote:

- struct msg_msg *volatile r_msg;
+ struct msg_msg *r_msg;

+ wake_q_add(wake_q, msr->r_tsk);
msr->r_msg = msg;
+ /*
+ * Rely on the implicit cmpxchg barrier from
+ * wake_q_add such that we can ensure that

Davidlohr, didn't you want to make that cmpxchg_relaxed() or
cmpxchg_release() ?

Right, I had forgotten about that. iirc we ended up deciding to fully
relax the cmpxchg and update the callers instead.
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