2017-10-05 14:54 GMT+02:00 Will Deacon <will.dea...@arm.com>: > > Hi all, > > This patch series reworks bits of the qrwlock code that it can be used > to replace the asm rwlocks currently implemented for arm64. The structure > of the series is: > > Patches 1-3 : Work WFE into qrwlock using atomic_cond_read_acquire so > we can avoid busy-waiting. > > Patch 4 : Enable qrwlocks for arm64 > > Patch 5-6 : Ensure writer slowpath fairness. This has a potential > performance impact on the writer unlock path, so I've > kept them at the end. > > The patches apply on top of my other locking cleanups: > > > http://lkml.kernel.org/r/1507055129-12300-1-git-send-email-will.dea...@arm.com > > although the conflict with mainline is trivial to resolve without those. > The full stack is also pushed here: > > git://git.kernel.org/pub/scm/linux/kernel/git/will/linux.git qrwlock > > All comments (particularly related to testing and performance) welcome!
Hi Will, run your patches on ThunderX2. Old RW locks: insmod ./locktorture.ko nwriters_stress=56 nreaders_stress=224 torture_type="rw_lock_irq" stat_interval=2 [ 558.700042] Writes: Total: 10127 Max/Min: 0/0 Fail: 0 [ 558.700054] Reads : Total: 764714 Max/Min: 0/0 Fail: 0 [ 561.797011] Writes: Total: 11288 Max/Min: 0/0 Fail: 0 [ 561.802518] Reads : Total: 2104452 Max/Min: 0/0 Fail: 0 [ 565.844219] Writes: Total: 11512 Max/Min: 0/0 Fail: 0 [ 565.849710] Reads : Total: 4277492 Max/Min: 0/0 Fail: 0 Queued RW locks: [ 221.491207] Writes: Total: 57318 Max/Min: 0/0 Fail: 0 [ 221.491219] Reads : Total: 382979 Max/Min: 0/0 Fail: 0 [ 223.507065] Writes: Total: 83490 Max/Min: 0/0 Fail: 0 [ 223.512611] Reads : Total: 684848 Max/Min: 0/0 Fail: 0 [ 225.522937] Writes: Total: 110012 Max/Min: 0/0 Fail: 0 [ 225.528511] Reads : Total: 968826 Max/Min: 0/0 Fail: 0 So readers are still preferred over writers, but results are _way_ better. Also, with the old implementation above test hung the machine which does not happen with the queued variant. If you want you can add: Tested-by: Jan Glauber <jglau...@cavium.com> --Jan > Cheers, > > Will > > --->8 > > Will Deacon (6): > kernel/locking: Use struct qrwlock instead of struct __qrwlock > locking/atomic: Add atomic_cond_read_acquire > kernel/locking: Use atomic_cond_read_acquire when spinning in qrwlock > arm64: locking: Move rwlock implementation over to qrwlocks > kernel/locking: Prevent slowpath writers getting held up by fastpath > kernel/locking: Remove unused union members from struct qrwlock > > arch/arm64/Kconfig | 17 ++++ > arch/arm64/include/asm/Kbuild | 1 + > arch/arm64/include/asm/spinlock.h | 164 > +------------------------------- > arch/arm64/include/asm/spinlock_types.h | 6 +- > include/asm-generic/atomic-long.h | 3 + > include/asm-generic/qrwlock.h | 14 +-- > include/asm-generic/qrwlock_types.h | 2 +- > include/linux/atomic.h | 4 + > kernel/locking/qrwlock.c | 83 +++------------- > 9 files changed, 43 insertions(+), 251 deletions(-) > > -- > 2.1.4 >
