On Mon, 25 Jan 2010 16:58:10 -0800 "H. Peter Anvin" <hpa@xxxxxxxxx> wrote: > On 01/25/2010 04:40 PM, Andrew Morton wrote: > > > > The problem is that arch/x86/include/asm/proto.h implements private > > rounding macros. The right way to fix that is to convert each x86 > > "call site" over to using the standard macros from kernel.h, then > > finally remove the private definitions from > > arch/x86/include/asm/proto.h. Don't just copy them over to kernel.h > > and make things muddier than they already are! > > > > If during that conversion it is found that the standard macros for some > > reason don't suit the x86 usage sites then please propose > > enhancements/fixes to the existing kernel.h facilities. > > > > They don't. > > The kernel-global alignment macros assume that either the alignment > datum (divisor) is a constant, or that it is acceptable to take the hit > of a division. Unfortunately, we have real use cases where the > alignment (guaranteed to be a power of two) is variable, but we don't > want to take the hit of a full-blown division. > > I suspect the global kernel tree has those, too, but it would seem to be > a dramatic change to change to change the existing facilities to assume > power of two alignment... > OK. And yes, rounding up or down to a power-of-two alignment is surely a common case. The rounding-up case is already handled by ALIGN(), is it not? round_up() is a quite poor name for a facility which will quietly fail if passed a non-power-of-2 argument! So I'd suggest that we see a standalone patch which adds the suitably-named and suitably-documented features to kernel.h. I'd be OK with merging such a patch into 2.6.33-rc, btw. As there is probably a lot of code which would benefit from being janitorially converted to these factilities, the patch should be well-reviewed and not hidden in an x86 patchbomb! There might be merit in adding a debug-only runtime check to ensure that the alignment mask really is a power-of-two, to assist such janitorial conversions, dunno. -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
