tree ce3bdf6c0379fdab8c72085f885402751fadea52
parent db3a8920995484e5e9a0abaf3bad2c7311b163db
author Paul E. McKenney <paulmck@linux.vnet.ibm.com> 1288084300 -0700
committer Paul E. McKenney <paulmck@linux.vnet.ibm.com> 1291096960 -0800

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>