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Date: Tue, 6 Apr 2010 17:54:15 +0100
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Avi Kivity <avi@redhat.com>, Darren Hart <dvhltc@us.ibm.com>,
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       Chris Mason <chris.mason@oracle.com>,
       John Cooper <john.cooper@third-harmonic.com>,
       Chris Wright <chrisw@sous-sol.org>
Subject: Re: [PATCH V2 0/6][RFC] futex: FUTEX_LOCK with optional adaptive
 spinning
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> > IMO the best solution is to spin in userspace while the lock holder is
> > running, fall into the kernel when it is scheduled out.
> 
> That's just not realistic as user space has no idea whether the lock
> holder is running or not and when it's scheduled out without a syscall :)

Which is the real problem that wants addressing and can be addressed very
cheaply. That would bring us up to par with 1970s RTOS environments ;)

Alan