Re: [RFC patch] spindep: add cross cache lines checking

[Arnd Bergmann]

On Monday 05 March 2012, Alex Shi wrote:
> Subject: [PATCH] lockdep: add cross cache lines checking
> 
> Modern x86 CPU won't hold whole memory bus when executing 'lock'
> prefixed instructions unless the instruction destination is crossing 2
> cache lines. If so, it is disaster of system performance.
> 
> Actually if the lock is not in the 'packed' structure, gcc places it
> safely under x86 arch. But seems add this checking in
> CONFIG_DEBUG_LOCK_ALLOC is harmless.

Have you tried making this a compile-time check using __alignof__?
I would say that any spinlock in a packed data structure is
basically a bug, even more so on most other architectures besides
x86.

	Arnd
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