[PATCH v2 3/3] ARM: Add barriers to the I/O accessorsifARM_DMA_MEM_BUFFERABLE

[Russell King - ARM Linux]

On Fri, Jul 09, 2010 at 03:21:23PM +0100, Catalin Marinas wrote:
> The patch below changes the __raw_* accessors to inline functions. Do
> you see any problem with this? This would be needed even without the I/O
> ordering patches.

I'd suggest you try building a kernel before and after this patch and
compare the sizes - and then look at the disassembly associated with
these accessors.

Certainly previous gcc versions generated useless instruction overhead
when these were inline functions - partly down to it wanting to make
sure things passed to/from __raw_writeb() and __raw_readb() were
absolutely definitely only 8-bit in size, and partly because this
seems to destroy GCC's ability to spot commonalities between multiple
accesses.

That's the reason why I've never pushed a patch which causes read[bwl]
and write[bwl] to check their arguments a little more strictly - I
found that it caused gcc to generate worse code for these accessors.