On Thu, Sep 1, 2011 at 9:14 PM, Thomas Gleixner [off-list ref] wrote:

On Fri, 26 Aug 2011, John Kacur wrote:

quoted

Problem:
make O=/bld/3.0.3-rt11/ kernel/fork.o
/home/jkacur/jk-2.6/kernel/fork.c:91: error: section of ‘name’ conflicts with previous declaration

__cacheline_aligned is already part of the definition of DEFINE_RWLOCK
for -rt

However it is not always used for the tasklist_lock in non-rt, so it can't
simply be added to the definition of DEFINE_RWLOCK in non-rt, so I modified
the definition in fork.c

-ENOPARSE

The real question is whether RWLOCKS should be cacheline aligned in
general or the RT addon is just overkill. Slapping an ifdef around
does not answer that.

Right, this was just a "put out a build-break fire" for now patch and
not a good long term patch. I noticed that of all the mainline
DEFINE_RWLOCKs that only the tasklist_lock is cache aligned. I'm
wondering if there is a reason for that, or just more of a historical
accident.

Regarding cache aligning the rwlocks in -rt, I also can't find the
historical reason for it, do you remember if it was for latency
performance, or did we have a atomicity issue on some architectures
when we didn't cache align it?

Thanks
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