[ECOS] Is it the right forum?

Nick Garnett nickg@redhat.com
Mon Dec 10 03:46:00 GMT 2001

Jonathan Larmour <jlarmour@redhat.com> writes:

> Dan Conti wrote:
> > 
> > Were the mutex optimization patch to be applied, i'd be more than happy
> > to provide ARM hal support.
> > 
> > Is the issue that Luoqi is uninterested in doing the copyright
> > assignment, or just one of those never got around to it things?
> Well I know Nick is unhappy with the patch as it stands, but we can work
> through that I would hope. But there's no point even trying unless we know
> we can accept the code. Luoqi has expressed interest in the assignment. No
> doubt it's the usual problem that it's the company lawyers who hold it up.
> Red Hat haven't exactly got a mega-responsive legal department either :-|.

For the record, my reasons for being unhappy with the patch are:

- It conflicts with my own plans for a spinlock based mutex
  implementation. A spinlock implementation and the current
  implementation can be combined fairly seamlessly, whereas the
  compare-and-swap version would have to exist as an alternative, with
  the maintenance problems that entails. The mutex code is already
  getting to be a maze of twisty little ifdefs, I want to avoid more.

- Compare-And-Swap is not supported on all architectures - the ARM is
  one of those. Even where support is available in the architecture,
  it is often omitted in the embedded variants that we have to run
  on. I am reluctant to introduce changes into generic code that can
  only be used on a limited range of targets.

- I am unhappy about some of the asumptions made in the code.
  Specifically: that the least significant bit of a pointer is
  available for the "want" bit, and that a pointer will fit into the
  size of data object controlled by compare-and-swap.

Nick Garnett, eCos Kernel Architect
Red Hat, Cambridge, UK

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