On 02/10/2019 09:00 PM, 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 27,373 29,409 28,170 28,773 30,164 29,276 > 2 7,697 14,922 1,703 7,435 15,167 1,729 > 4 6,987 14,285 1,490 7,181 14,438 1,330 > 8 6,650 13,652 761 6,918 13,796 718 > 16 6,434 15,729 713 6,554 16,030 625 > 32 5,590 15,312 552 6,124 15,344 471 > 64 5,980 15,478 61 5,668 15,509 58 > > 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 liitle bit > faster than the assembly version especially for read-lock and when lock > contention is low. 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 > 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> I have decided to break the rwsem patchset that I sent out on last Thursday into 3 parts. This patch is part 0 as it touches a number of arch specific files and so have the widest distribution. I would like to get it merged first. Part 1 will be patches 1-10 (except 4) of my original rwsem patchset. This part moves things around, adds more debugging capability and lays the ground work for the next part. Part 2 will contains the remaining patches which are the real beef of the whole patchset. Cheers, Longman
