In this patchset, we introduce two optimizations to read write semaphore.
The first one reduces cache bouncing of the sem->count field
by doing a pre-read of the sem->count and avoid cmpxchg if possible.
The second patch introduces similar optimistic spining logic in
the mutex code for the writer lock acquisition of rw-sem.
Combining the two patches, in testing by Davidlohr Bueso on aim7 workloads
on 8 socket 80 cores system, he saw improvements of
alltests (+14.5%), custom (+17%), disk (+11%), high_systime
(+5%), shared (+15%) and short (+4%), most of them after around 500
users when i_mmap was implemented as rwsem.
Feedbacks on the effectiveness of these tweaks on other workloads
will be appreciated.
Alex Shi (1):
rwsem: check the lock before cpmxchg in down_write_trylock and
rwsem_do_wake
Tim Chen (1):
rwsem: do optimistic spinning for writer lock acquisition
Makefile | 2 +-
include/asm-generic/rwsem.h | 8 +-
include/linux/rwsem.h | 3 +
init/Kconfig | 9 +++
kernel/rwsem.c | 29 +++++++-
lib/rwsem.c | 169 ++++++++++++++++++++++++++++++++++++++-----
6 files changed, 195 insertions(+), 25 deletions(-)
--
1.7.4.4
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