* Waiman Long <longman@xxxxxxxxxx> wrote: > 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. Sounds good to me - I've merged this patch, will push it out after testing. Thanks, Ingo
