diff options
| author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2011-01-07 02:33:47 -0800 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2011-01-14 04:56:49 -0800 |
| commit | c072a388d59a1d48e36864d0e66f42d71745be1c (patch) | |
| tree | a0537c767c834d1846430ab3bb4eb83c0d0923d7 | |
| parent | 394f4528c523d88daabd50f883a8d6b164075555 (diff) | |
rcu: demote SRCU_SYNCHRONIZE_DELAY from kernel-parameter status
Because the adaptive synchronize_srcu_expedited() approach has
worked very well in testing, remove the kernel parameter and
replace it by a C-preprocessor macro. If someone finds problems
with this approach, a more complex and aggressively adaptive
approach might be required.
Longer term, SRCU will be merged with the other RCU implementations,
at which point synchronize_srcu_expedited() will be event driven,
just as synchronize_sched_expedited() currently is. At that point,
there will be no need for this adaptive approach.
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| -rw-r--r-- | init/Kconfig | 15 | ||||
| -rw-r--r-- | kernel/srcu.c | 15 |
2 files changed, 13 insertions, 17 deletions
diff --git a/init/Kconfig b/init/Kconfig index 526ec1c7456a..e11bc793a91d 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -497,21 +497,6 @@ config RCU_BOOST_DELAY Accept the default if unsure. -config SRCU_SYNCHRONIZE_DELAY - int "Microseconds to delay before waiting for readers" - range 0 20 - default 10 - help - This option controls how long SRCU delays before entering its - loop waiting on SRCU readers. The purpose of this loop is - to avoid the unconditional context-switch penalty that would - otherwise be incurred if there was an active SRCU reader, - in a manner similar to adaptive locking schemes. This should - be set to be a bit longer than the common-case SRCU read-side - critical-section overhead. - - Accept the default if unsure. - endmenu # "RCU Subsystem" config IKCONFIG diff --git a/kernel/srcu.c b/kernel/srcu.c index 98d8c1e80edb..73ce23feaea9 100644 --- a/kernel/srcu.c +++ b/kernel/srcu.c @@ -156,6 +156,16 @@ void __srcu_read_unlock(struct srcu_struct *sp, int idx) EXPORT_SYMBOL_GPL(__srcu_read_unlock); /* + * We use an adaptive strategy for synchronize_srcu() and especially for + * synchronize_srcu_expedited(). We spin for a fixed time period + * (defined below) to allow SRCU readers to exit their read-side critical + * sections. If there are still some readers after 10 microseconds, + * we repeatedly block for 1-millisecond time periods. This approach + * has done well in testing, so there is no need for a config parameter. + */ +#define SYNCHRONIZE_SRCU_READER_DELAY 10 + +/* * Helper function for synchronize_srcu() and synchronize_srcu_expedited(). */ static void __synchronize_srcu(struct srcu_struct *sp, void (*sync_func)(void)) @@ -207,11 +217,12 @@ static void __synchronize_srcu(struct srcu_struct *sp, void (*sync_func)(void)) * will have finished executing. We initially give readers * an arbitrarily chosen 10 microseconds to get out of their * SRCU read-side critical sections, then loop waiting 1/HZ - * seconds per iteration. + * seconds per iteration. The 10-microsecond value has done + * very well in testing. */ if (srcu_readers_active_idx(sp, idx)) - udelay(CONFIG_SRCU_SYNCHRONIZE_DELAY); + udelay(SYNCHRONIZE_SRCU_READER_DELAY); while (srcu_readers_active_idx(sp, idx)) schedule_timeout_interruptible(1); |