Re: [patch 2/6 -rt] powerpc 2.6.20-rt8: to convert spinlocks to raw ones.

[Paul Mackerras <paulus@samba.org>]

Bill Huey (hui) writes:

> The places that need to be reverted to raw spinlocks are generally either
> acquired by function calls that allocate the spinlock at a terminal of the
> kernel's lock graph or isolated from other callers completely (parts of the
> timer for logic for instance). It's all about the collision of various lock
> (preemptive and non-preemptive) subtrees and how to avoid scheduling within
> atomic violations that lead to deadlocks. The -rt patch gets arbitrary
> preemption abilities by shrinking the non-preemptive sub-tree bit to the bare
> essentials of what will let a system to run yet still preserve all of
> the expected locking semantics of a critical section.

Thanks; that's an interesting explanation.

It misses the point of what I was saying to Sergei, though, which was
*not* "I don't understand your patch", it was "if this patch goes into
a git tree, someone coming along in 3 years time won't understand the
patch."  In other words I was ranting about the need for a decent
description to accompany the patch itself, so it would go into the
permanent record.

Regards,
Paul.