linux-kernel - Re: [RFC PATCH 0/7] priority-boost urcu

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Message-ID: <4E521D0B.7030000@redhat.com>
Date:	Mon, 22 Aug 2011 11:10:35 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	ltt-dev@...ts.casi.polymtl.ca, rp@...s.cs.pdx.edu,
	Darren Hart <darren@...art.com>, Ingo Molnar <mingo@...e.hu>,
	tglx@...utronix.de, Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 0/7] priority-boost urcu

On 08/18/2011 03:30 PM, Steven Rostedt wrote:
>>  In QEMU I added the manual-reset event and use it in the
>>  implementation of RCU.

That was me. :)

> Be careful with this. You better make sure that Microsoft does not hold
> any patents to this method, otherwise all your work will be in vain.

I found the synchronization primitive mentioned in a patent filed 1994, 
so I would be surprised if the primitive itself is younger than 20 years 
(or even younger than 30 years in fact).

The only possibly novel thing is the userspace-only path when there is 
no contention.  Windows events always do a system call, so there is some 
hope it isn't patented.

But if Microsoft did have a patent and it applied, both the 
userspace-RCU and QEMU code would have a problem.  The technique is the 
same independent of whether you call futex primitives directly, or you 
wrap them in an API.

Paolo
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