On Fri, May 09, 2014 at 08:32:41PM +0200, Hans-Christian Egtvedt wrote: > Around Thu 08 May 2014 15:58:46 +0200 or thereabout, Peter Zijlstra wrote: > > Many of the atomic op implementations are the same except for one > > instruction; fold the lot into a few CPP macros and reduce LoC. > > The add and sub atomic operations are not 100% the same. Sub has more > constraints on the integer size than add. Sub only takes a signed 21-bit > integer, while add can do 32-bit additions IIRC correctly the instructions > for AVR32. > > This is why you see in atomic_sub_return() that i is typed as "rKs21", while > in atomic_add_return, i is typed "r". > > Your change limits both atomic operations to work only on signed 21-bit > integers. Urgh, fail on me for not seeing that. > > - if (__builtin_constant_p(i) && (i >= -1048575) && (i <= 1048576)) > > - result = atomic_sub_return(-i, v); > > I do not recall why we did it like this any more, I would assume both sub and > add to be single cycle instructions. Right and if its a constant the negate is compile time too. OK, so if I only generate add and provide inline stubs to implement sub with add this should be good again, right? Any other instructions I should be careful with? I take it the bit ops are full 32 bits again? -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
