* Russell King - ARM Linux <li...@arm.linux.org.uk> wrote:
> On Thu, Oct 22, 2015 at 05:09:59PM +0200, Peter Zijlstra wrote:
> > Hmm, I was sure I send a reply, but I cannot even find it in my own sent
> > folder so who knows.
> >
> > My current preference is to keep the thing a macro and work around it in
> > the usage site because while these warns are annoying, they're at least
> > visible. Whereas, with an inline, code bloat is entirely silent. Even if
> > the sites you found are harmless, there's no saying what the future will
> > bring etc..
>
> I agree - we've got way too many inline functions already. My biggest
> annoyance
> in that respect is the asm-generic dma_map_single() implementation that we're
> now forced to use on ARM, which results in quite a large chunk of code at
> every
> callsite.
>
> The problem there is that when you have drivers which do something like:
>
> dma = dma_map_single(dev, page_address(page), size, dir);
>
> you end up with code which converts the struct page to a virtual address, and
> then you end up with code in the dma_map_single() inline function which then
> converts it back to a struct page + offset - none of which, with modern ARM
> kernels, the compiler has a hope in hell of optimising.
>
> So we end up with all that junk at every single dma_map_single() callsite. If
> dma_map_single() were a library function, it would be a lot smaller since
> we'd
> only have one copy of the complex virt->struct page conversion.
Should be pretty easy to fix, once you know which inline functions hurt.
Thanks,
Ingo
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