1 files changed, 38 insertions, 0 deletions

diff --git a/patches/boot_time_opt_guest/0103-sysrq-skip-synchronize_rcu-if-there-is-no-old-op.patch b/patches/boot_time_opt_guest/0103-sysrq-skip-synchronize_rcu-if-there-is-no-old-op.patch
new file mode 100644
index 0000000..d3a20fb
--- /dev/null
+++ b/patches/boot_time_opt_guest/0103-sysrq-skip-synchronize_rcu-if-there-is-no-old-op.patch
@@ -0,0 +1,38 @@
+From 7be707833bb35c295eb702d13cf73ac9390e4b31 Mon Sep 17 00:00:00 2001
+From: Arjan van de Ven <arjan@linux.intel.com>
+Date: Wed, 11 Feb 2015 16:25:16 -0600
+Subject: [PATCH 103/114] sysrq: skip synchronize_rcu() if there is no old op
+
+synchronize_rcu() is expensive. Currently it is called as part of the sysrq
+registration/unregistration, which happens during boot several times.
+Now, the reason for the synchronize_rcu() is to allow an old registered
+operation to expire properly... which is pointless if the old operation
+is NULL...
+So we can save the common case of the old operation being NULL a lot of time
+by just checking for non-NULL prior to the synchronize_rcu()
+
+Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
+Signed-off-by: Miguel Bernal Marin <miguel.bernal.marin@linux.intel.com>
+---
+ drivers/tty/sysrq.c | 4 +++-
+ 1 file changed, 3 insertions(+), 1 deletion(-)
+
+diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
+index 701c085bb19b..c60c7ba57ad9 100644
+--- a/drivers/tty/sysrq.c
++++ b/drivers/tty/sysrq.c
+@@ -1065,8 +1065,10 @@ static int __sysrq_swap_key_ops(int key, struct sysrq_key_op *insert_op_p,
+         * A concurrent __handle_sysrq either got the old op or the new op.
+         * Wait for it to go away before returning, so the code for an old
+         * op is not freed (eg. on module unload) while it is in use.
++        * This is only relevant if the old op is not NULL of course.
+         */
+-       synchronize_rcu();
++       if (remove_op_p)
++               synchronize_rcu();
+ 
+        return retval;
+ }
+-- 
+2.11.1
+