On Wed, Feb 13, 2019 at 05:00:15PM -0500, Waiman Long wrote: > As the generic rwsem-xadd code is using the appropriate acquire and > release versions of the atomic operations, the arch specific rwsem.h > files will not be that much faster than the generic code as long as the > atomic functions are properly implemented. So we can remove those arch > specific rwsem.h and stop building asm/rwsem.h to reduce maintenance > effort. > > Currently, only x86, alpha and ia64 have implemented architecture > specific fast paths. I don't have access to alpha and ia64 systems for > testing, but they are legacy systems that are not likely to be updated > to the latest kernel anyway. > > By using a rwsem microbenchmark, the total locking rates on a 4-socket > 56-core 112-thread x86-64 system before and after the patch were as > follows (mixed means equal # of read and write locks): > > Before Patch After Patch > # of Threads wlock rlock mixed wlock rlock mixed > ------------ ----- ----- ----- ----- ----- ----- > 1 29,201 30,143 29,458 28,615 30,172 29,201 > 2 6,807 13,299 1,171 7,725 15,025 1,804 > 4 6,504 12,755 1,520 7,127 14,286 1,345 > 8 6,762 13,412 764 6,826 13,652 726 > 16 6,693 15,408 662 6,599 15,938 626 > 32 6,145 15,286 496 5,549 15,487 511 > 64 5,812 15,495 60 5,858 15,572 60 > > There were some run-to-run variations for the multi-thread tests. For > x86-64, using the generic C code fast path seems to be a little bit > faster than the assembly version with low lock contention. Looking at > the assembly version of the fast paths, there are assembly to/from C > code wrappers that save and restore all the callee-clobbered registers > (7 registers on x86-64). The assembly generated from the generic C > code doesn't need to do that. That may explain the slight performance > gain here. > > The generic asm rwsem.h can also be merged into kernel/locking/rwsem.h > with no code change as no other code other than those under > kernel/locking needs to access the internal rwsem macros and functions. > > Signed-off-by: Waiman Long <longman@xxxxxxxxxx> > --- > MAINTAINERS | 1 - > arch/alpha/include/asm/rwsem.h | 211 ----------------------------------- > arch/arm/include/asm/Kbuild | 1 - > arch/arm64/include/asm/Kbuild | 1 - > arch/hexagon/include/asm/Kbuild | 1 - > arch/ia64/include/asm/rwsem.h | 172 ----------------------------- > arch/powerpc/include/asm/Kbuild | 1 - > arch/s390/include/asm/Kbuild | 1 - > arch/sh/include/asm/Kbuild | 1 - > arch/sparc/include/asm/Kbuild | 1 - > arch/x86/include/asm/rwsem.h | 237 ---------------------------------------- > arch/x86/lib/Makefile | 1 - > arch/x86/lib/rwsem.S | 156 -------------------------- > arch/x86/um/Makefile | 1 - > arch/xtensa/include/asm/Kbuild | 1 - > include/asm-generic/rwsem.h | 140 ------------------------ > include/linux/rwsem.h | 4 +- > kernel/locking/percpu-rwsem.c | 2 + > kernel/locking/rwsem.h | 130 ++++++++++++++++++++++ > 19 files changed, 133 insertions(+), 930 deletions(-) > delete mode 100644 arch/alpha/include/asm/rwsem.h > delete mode 100644 arch/ia64/include/asm/rwsem.h > delete mode 100644 arch/x86/include/asm/rwsem.h > delete mode 100644 arch/x86/lib/rwsem.S > delete mode 100644 include/asm-generic/rwsem.h Looks like a nice cleanup, thanks: Acked-by: Will Deacon <will.deacon@xxxxxxx> Will
