linux-kernel - Re: [PATCH v2 2/3] mutex: add support for reservation style locks, v2

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Date:	Thu, 04 Apr 2013 18:46:05 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Daniel Vetter <daniel@...ll.ch>
Cc:	Maarten Lankhorst <maarten.lankhorst@...onical.com>,
	linux-arch@...r.kernel.org, daniel.vetter@...ll.ch, x86@...nel.org,
	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	linaro-mm-sig@...ts.linaro.org, robclark@...il.com,
	tglx@...utronix.de, mingo@...e.hu, linux-media@...r.kernel.org
Subject: Re: [PATCH v2 2/3] mutex: add support for reservation style locks,
 v2

On Thu, 2013-04-04 at 15:31 +0200, Daniel Vetter wrote:
> I'm a bit confused about the different classes you're talking about.
> Since
> the ticket queue is currently a global counter there's only one class
> of
> ww_mutexes. 

Right, so that's not something that's going to fly.. we need to support
multiple users, including nesting of those. Again, you're adding
something to the generic kernel infrastructure, it had better be usable
:-)

> I guess we could change that once a second user shows up

No, we fix that before it all goes in. I would _so_ hate to find out it
cannot be 'fixed' and be stuck with a half-arsed sync primitive in the
core kernel that's only every usable by the one existent user.

So for now, forget all about TTM, DMA-BUF and other such coolness
except to verify that whatever we end up with does indeed work for the
case you need it for ;-)

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