Ingo Molnar wrote: > > Apparently it messes up with asm()s: it doesnt know the contents of the > asm() and hence it over-estimates the size [based on string heuristics] > ... > Right. gcc simply doesn't have any way to know how heavyweight an asm() statement is, and it WILL do the wrong thing in many cases -- especially the ones which involve an out-of-line recovery stub. This is due to a fundamental design decision in gcc to not integrate the compiler and assembler (which some compilers do.) > Which is bad - asm()s tend to be the most important entities to inline - > all over our fastpaths . > > Despite that messup it's still a 1% net size win: > > text data bss dec hex filename > 7109652 1464684 802888 9377224 8f15c8 vmlinux.always-inline > 7046115 1465324 802888 9314327 8e2017 vmlinux.optimized-inlining > > That win is mixed in slowpath and fastpath as well. The good part here is that the assembly ones really don't have much subtlety -- a function call is at least five bytes, usually more once you count in the register spill penalties -- so __always_inline-ing them should still end up with numbers looking very much like the above. > I see three options: > > - Disable CONFIG_OPTIMIZE_INLINING=y altogether (it's already > default-off) > > - Change the asm() inline markers to something new like asm_inline, which > defaults to __always_inline. > > - Just mark all asm() inline markers as __always_inline - realizing that > these should never ever be out of line. > > We might still try the second or third options, as i think we shouldnt go > back into the business of managing the inline attributes of ~100,000 > kernel functions. > > I'll try to annotate the inline asms (there's not _that_ many of them), > and measure what the size impact is. The main reason to do #2 over #3 would be for programmer documentation. There simply should be no reason to ever out-of-lining these. However, documenting the reason to the programmer is a valuable thing in itself. -hpa -- H. Peter Anvin, Intel Open Source Technology Center I work for Intel. I don't speak on their behalf. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
