call_rcu: use futex for wakeup scheme
authorMathieu Desnoyers <mathieu.desnoyers@efficios.com>
Tue, 7 Jun 2011 04:16:00 +0000 (00:16 -0400)
committerMathieu Desnoyers <mathieu.desnoyers@efficios.com>
Tue, 7 Jun 2011 04:16:00 +0000 (00:16 -0400)
commit263e3cf98bd9b7e6b352e25b8007bd1b6df250b8
tree476a5ca2782fe3b985e7e0064e8b95562e377b2a
parentc1d2c60b1c754815d27f29705d5f2077c0900148
call_rcu: use futex for wakeup scheme

If I remove the URCU_CALL_RCU_RT flag from the rbtree single writer
test, thus using the pthread_cond_signal mechanism, there is a huge
slowdown: without cpu affinity for the worker threads, it crawls to 129
updates/s (looks like mutex contention between the thread calling
call_rcu and the call_rcu thread). Adding CPU affinity to the per-cpu
call_rcu threads, I get 546 updates/s, which is slightly better (better
cache locality, and maybe the mutex contention is not as bad thanks to
the two threads sharing the same CPU).

So I decided to try replacing pthread_cond_wait/signal with my
futex-based implementation I use for the rest of the urcu lib: it has
the advantage of removing the mutex from the call_rcu() execution
entirely, sampling the "futex" variable without any mutex whatsoever for
the case where no wakeup is needed.

Disabling URCU_CALL_RCU_RT flag, with per-cpu affined call_rcu threads,
with my futex-based wakeup implementation, I get 55754 updates/s (even
better than with URCU_CALL_RCU_RT flag!).

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
urcu-call-rcu-impl.h
This page took 0.02456 seconds and 4 git commands to generate.