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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2010-10-26 02:11:40 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2010-11-29 22:02:40 -0800
commit46fdb0937f26124700fc9fc80da4776330cc00d3 (patch)
treece3bdf6c0379fdab8c72085f885402751fadea52 /init
parentdb3a8920995484e5e9a0abaf3bad2c7311b163db (diff)
downloadlinux-2.6.38-lt-ux500-46fdb0937f26124700fc9fc80da4776330cc00d3.tar.gz
rcu: Make synchronize_srcu_expedited() fast if running readers
The synchronize_srcu_expedited() function is currently quick if there are no active readers, but will delay a full jiffy if there are any. If these readers leave their SRCU read-side critical sections quickly, this is way too long to wait. So this commit first waits ten microseconds, and only then falls back to jiffy-at-a-time waiting. Reported-by: Avi Kivity <avi@redhat.com> Reported-by: Marcelo Tosatti <mtosatti@redhat.com> Tested-by: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'init')
-rw-r--r--init/Kconfig15
1 files changed, 15 insertions, 0 deletions
diff --git a/init/Kconfig b/init/Kconfig
index 929adf6cb6b..35518243c4b 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -488,6 +488,21 @@ 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