On Wed, 2015-06-10 at 17:57 +0200, Ralf Baechle wrote: > On Wed, Jun 10, 2015 at 04:58:04PM +0200, Ralf Baechle wrote: > > > On Mon, Jun 08, 2015 at 03:14:43PM +0200, Xose Vazquez Perez wrote: > > > > > If there is anything wrong, please report it in this thread: > > > https://marc.info/?t=143332955700003 > > > > > > > locking/ cmpxchg-local : TODO | HAVE_CMPXCHG_LOCAL # arch supports the this_cpu_cmpxchg() API > > > > This one was easy - we have the functions in the code just no "select > > HAVE_CMPXCHG_LOCAL" Kconfig. > > Something's wrong there. The new file > Documentation/features/locking/cmpxchg-local/arch-support.txt in linux-next > claims correctly that only s390 and x86 define HAVE_CMPXCHG_LOCAL. And a > git grep -w cmpxchg_local finds that in addition to these alpha, arm, arm64, > avr32, blackfin, c6x, frv, ia64, m32r, m68k, mips, parisc, powerpc, sparc, > unicore32 and xtensa define cmpxchg_local. > > These architectures seem to not define cmpxchg_local in their arch/ dir: > > arc cris hexagon metag microblaze mn10300 nios2 openrisc score sh tile um > > Microblaze and nios2 include <asm-generic/cmpxchg.h> into their arch > cmpxchg.h so they get a definition of these functions but don't define > HAVE_CMPXCHG_LOCAL. Peter Zijlstra said it the local versions are ~ 20 > cycles faster on x86 than the "global" version. But I've found one user > of cmpxchg_local, mm/vmstat.c and one user of cmpxchg64_local, > drivers/iommu/intel-iommu.c. Sure, fixing the issue was trivial for me > on MIPS but is having cmpxchg{,64}_local actually worth it? If you traverse the obfuscation chain a little, you'll find that local_cmpxchg() is implemented using cmpxchg_local(), and there are a few more users of that.
