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

On Thu, Mar 08, 2007 at 02:26:47PM +1100, Paul Mackerras wrote:

Bill Huey (hui) writes:

quoted

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.

Yeah, I think it's a a fear and uncertainly about the technical details about
the patch. That is why folks CC Ingo and company to get either a kind of
confirmation that this is ok along with comments. There are very few folks
that really understand the basic principals of the patch in this community
and that's not going to change any time soon. The mystery, paranoia (FUD)
and criticism surrounding it can make folks a bit shy.

I'll talk to you and Ben about it if we all get to OLS again. :)

bill