This patch set improves upon the rwsem optimistic spinning patch set
from Davidlohr to enable better performing rwsem and more aggressive
use of optimistic spinning.
By using a microbenchmark running 1 million lock-unlock operations per
thread on a 4-socket 40-core Westmere-EX x86-64 test machine running
3.16-rc7 based kernels, the following table shows the execution times
with 2/10 threads running on different CPUs on the same socket where
load is the number of pause instructions in the critical section:
lock/r:w ratio # of threads Load:Execution Time (ms)
-------------- ------------ ------------------------
mutex 2 1:530.7, 5:406.0, 10:472.7
mutex 10 1:1848 , 5:2046 , 10:4394
Before patch:
rwsem/0:1 2 1:339.4, 5:368.9, 10:394.0
rwsem/1:1 2 1:2915 , 5:2621 , 10:2764
rwsem/10:1 2 1:891.2, 5:779.2, 10:827.2
rwsem/0:1 10 1:5618 , 5:5722 , 10:5683
rwsem/1:1 10 1:14562, 5:14561, 10:14770
rwsem/10:1 10 1:5914 , 5:5971 , 10:5912
After patch:
rwsem/0:1 2 1:161.1, 5:244.4, 10:271.4
rwsem/1:1 2 1:188.8, 5:212.4, 10:312.9
rwsem/10:1 2 1:168.8, 5:179.5, 10:209.8
rwsem/0:1 10 1:1306 , 5:1733 , 10:1998
rwsem/1:1 10 1:1512 , 5:1602 , 10:2093
rwsem/10:1 10 1:1267 , 5:1458 , 10:2233
% Change:
rwsem/0:1 2 1:-52.5%, 5:-33.7%, 10:-31.1%
rwsem/1:1 2 1:-93.5%, 5:-91.9%, 10:-88.7%
rwsem/10:1 2 1:-81.1%, 5:-77.0%, 10:-74.6%
rwsem/0:1 10 1:-76.8%, 5:-69.7%, 10:-64.8%
rwsem/1:1 10 1:-89.6%, 5:-89.0%, 10:-85.8%
rwsem/10:1 10 1:-78.6%, 5:-75.6%, 10:-62.2%
It can be seen that there is dramatic reduction in the execution
times. The new rwsem is now even faster than mutex whether it is all
writers or a mixture of writers and readers.
Running the AIM7 benchmarks on the same 40-core system (HT off),
the performance improvements on some of the workloads were as follows:
Workload Before Patch After Patch % Change
-------- ------------ ----------- --------
custom (200-1000) 446135 477404 +7.0%
custom (1100-2000) 449665 484734 +7.8%
high_systime 152437 154217 +1.2%
(200-1000)
high_systime 269695 278942 +3.4%
(1100-2000)
Waiman Long (7):
locking/rwsem: don't resched at the end of optimistic spinning
locking/rwsem: more aggressive use of optimistic spinning
locking/rwsem: check for active writer/spinner before wakeup
locking/rwsem: threshold limited spinning for active readers
locking/rwsem: move down rwsem_down_read_failed function
locking/rwsem: enables optimistic spinning for readers
locking/rwsem: allow waiting writers to go back to optimistic spinning
include/linux/osq_lock.h | 5 +
include/linux/rwsem.h | 7 +
kernel/locking/rwsem-xadd.c | 328 ++++++++++++++++++++++++++++++++++---------
kernel/locking/rwsem.c | 17 ++-
4 files changed, 288 insertions(+), 69 deletions(-)
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