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Date: Thu, 6 Jul 2017 18:10:47 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: David Laight <David.Laight@ACULAB.COM>,
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Subject: Re: [PATCH v2 0/9] Remove spin_unlock_wait()
Message-ID: <20170706161047.nse2s4gquljv5bni@hirez.programming.kicks-ass.net>
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On Thu, Jul 06, 2017 at 08:21:10AM -0700, Paul E. McKenney wrote:
> And yes, there are architecture-specific optimizations for an
> empty spin_lock()/spin_unlock() critical section, and the current
> arch_spin_unlock_wait() implementations show some of these optimizations.
> But I expect that performance benefits would need to be demonstrated at
> the system level.

I do in fact contended there are any optimizations for the exact
lock+unlock semantics.

The current spin_unlock_wait() is weaker. Most notably it will not (with
exception of ARM64/PPC for other reasons) cause waits on other CPUs.