fcntl spinlock in Linux?

[Volker Lendecke]

On Thu, Jan 24, 2013 at 02:05:00PM +0100, Stefan (metze) Metzmacher wrote:
> > If that interpretation is right, then I guess with many
> > cores in a NUMA configuration fcntl locks are just a VERY,
> > VERY bad idea at all if you want to scale.
> > 
> > Please tell me that I am wrong :-)
> 
> Reading through
> http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=blob;f=Documentation/DocBook/kernel-locking.tmpl
> indicates to me that this could be solved using RCU to protect the
> global lock list.

Follow-up question: The process shared robust mutexes, do
they scale better? Or do we also sit on a central spinlock
when we really start beating the futex API?

I can't imagine futex() spins on one central lock, but I
also could not imagine that fcntl does, so I would like to
know about bad surprises before we put much effort into
annihilate fcntl.

Volker

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