On Thu, May 02, 2024 at 07:11:52AM +0200, John Paul Adrian Glaubitz wrote: > On Wed, 2024-05-01 at 22:06 -0700, Paul E. McKenney wrote: > > > Does cmpxchg_emu_u8() have any advantages over the native xchg_u8()? > > > > That would be 8-bit xchg() rather than 8-byte cmpxchg(), correct? > > Indeed. I realized this after sending my reply. No problem, as I do know that feeling! > > Or am I missing something subtle here that makes sh also support one-byte > > (8-bit) cmpxchg()? > > Is there an explanation available that explains the rationale behind the > series, so I can learn more about it? We have some places in mainline that need one-byte cmpxchg(), so this series provides emulation for architectures that do not support this notion. > Also, I am opposed to removing Alpha entirely as it's still being actively > maintained in Debian and Gentoo and works well. Understood, and this sort of compatibility consideration is why this version of this patchset does not emulate two-byte (16-bit) cmpxchg() operations. The original (RFC) series did emulate these, which does not work on a few architectures that do not provide 16-bit load/store instructions, hence no 16-bit support in this series. So this one-byte-only series affects only Alpha systems lacking single-byte load/store instructions. If I understand correctly, Alpha 21164A (EV56) and later *do* have single-byte load/store instructions, and thus are still just fine. In fact, it looks like EV56 also has two-byte load/store instructions, and so would have been OK with the original one-/two-byte RFC series. Arnd will not be shy about correcting me if I am wrong. ;-) > Adrian > > -- > .''`. John Paul Adrian Glaubitz > : :' : Debian Developer > `. `' Physicist > `- GPG: 62FF 8A75 84E0 2956 9546 0006 7426 3B37 F5B5 F913
