summaryrefslogtreecommitdiff
path: root/kernel/cpuset.c
diff options
context:
space:
mode:
authorPranith Kumar <bobby.prani@gmail.com>2014-08-12 13:07:47 -0400
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-11-21 09:23:05 -0800
commit42d49f4525661181162386eea643275a5de10b59 (patch)
treeb8b7a26ae7a189b79fc080b6d38e127f65e86e51 /kernel/cpuset.c
parent35cbd149f07864e5d68c8368549a03609fddd1a3 (diff)
rcu: Use rcu_gp_kthread_wake() to wake up grace period kthreads
commit 2aa792e6faf1a00f5accf1f69e87e11a390ba2cd upstream. The rcu_gp_kthread_wake() function checks for three conditions before waking up grace period kthreads: * Is the thread we are trying to wake up the current thread? * Are the gp_flags zero? (all threads wait on non-zero gp_flags condition) * Is there no thread created for this flavour, hence nothing to wake up? If any one of these condition is true, we do not call wake_up(). It was found that there are quite a few avoidable wake ups both during idle time and under stress induced by rcutorture. Idle: Total:66000, unnecessary:66000, case1:61827, case2:66000, case3:0 Total:68000, unnecessary:68000, case1:63696, case2:68000, case3:0 rcutorture: Total:254000, unnecessary:254000, case1:199913, case2:254000, case3:0 Total:256000, unnecessary:256000, case1:201784, case2:256000, case3:0 Here case{1-3} are the cases listed above. We can avoid these wake ups by using rcu_gp_kthread_wake() to conditionally wake up the grace period kthreads. There is a comment about an implied barrier supplied by the wake_up() logic. This barrier is necessary for the awakened thread to see the updated ->gp_flags. This flag is always being updated with the root node lock held. Also, the awakened thread tries to acquire the root node lock before reading ->gp_flags because of which there is proper ordering. Hence this commit tries to avoid calling wake_up() whenever we can by using rcu_gp_kthread_wake() function. Signed-off-by: Pranith Kumar <bobby.prani@gmail.com> CC: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Kamal Mostafa <kamal@canonical.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'kernel/cpuset.c')
0 files changed, 0 insertions, 0 deletions