linux-kernel - [PATCH 3/6] rcu,nohz: run vtime_user_enter/exit only when state == IN

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Date:	Mon,  9 Feb 2015 11:04:41 -0500
From:	riel@...hat.com
To:	paulmck@...ux.vnet.ibm.com
Cc:	linux-kernel@...r.kernel.org, catalin.marinas@....com,
	will.deacon@....com, fweisbec@...il.com, kvm@...r.kernel.org,
	mtosatti@...hat.com, borntraeger@...ibm.com, mingo@...nel.org,
	oleg@...hat.com, lcapitulino@...hat.com, pbonzini@...hat.com,
	Rik van Riel <riel@...hat.com>
Subject: [PATCH 3/6] rcu,nohz: run vtime_user_enter/exit only when state == IN_USER

From: Rik van Riel <riel@...hat.com>

Only run vtime_user_enter, vtime_user_exit, and the user enter & exit
trace points when we are entering or exiting user state, respectively.

The RCU code only distinguishes between "idle" and "not idle or kernel".
There should be no need to add an additional (unused) state there.

Signed-off-by: Rik van Riel <riel@...hat.com>
---
 kernel/context_tracking.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
index e031e8c0fb91..2d94147c07b2 100644
--- a/kernel/context_tracking.c
+++ b/kernel/context_tracking.c
@@ -77,7 +77,6 @@ void context_tracking_enter(enum ctx_state state)
 	local_irq_save(flags);
 	if ( __this_cpu_read(context_tracking.state) != state) {
 		if (__this_cpu_read(context_tracking.active)) {
-			trace_user_enter(0);
 			/*
 			 * At this stage, only low level arch entry code remains and
 			 * then we'll run in userspace. We can assume there won't be
@@ -85,7 +84,10 @@ void context_tracking_enter(enum ctx_state state)
 			 * user_exit() or rcu_irq_enter(). Let's remove RCU's dependency
 			 * on the tick.
 			 */
-			vtime_user_enter(current);
+			if (state == IN_USER) {
+				trace_user_enter(0);
+				vtime_user_enter(current);
+			}
 			rcu_user_enter();
 		}
 		/*
@@ -137,8 +139,10 @@ void context_tracking_exit(enum ctx_state state)
 			 * RCU core about that (ie: we may need the tick again).
 			 */
 			rcu_user_exit();
-			vtime_user_exit(current);
-			trace_user_exit(0);
+			if (state == IN_USER) {
+				vtime_user_exit(current);
+				trace_user_exit(0);
+			}
 		}
 		__this_cpu_write(context_tracking.state, IN_KERNEL);
 	}
-- 
1.9.3

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