linux-kernel - [PATCH 5/7] context_tracking: Run vtime_user_enter/exit only when state == CONTEXT

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Date:	Thu,  5 Mar 2015 03:14:54 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Rik van Riel <riel@...hat.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Alexander Graf <agraf@...e.de>,
	Luiz Capitulino <lcapitulino@...hat.com>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
	Andy Lutomirski <luto@...capital.net>,
	Will deacon <will.deacon@....com>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: [PATCH 5/7] context_tracking: Run vtime_user_enter/exit only when state == CONTEXT_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 KVM code in guest_enter and guest_exit already take care of calling
vtime_guest_enter and vtime_guest_exit, 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.

Reviewed-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Signed-off-by: Rik van Riel <riel@...hat.com>
Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Will deacon <will.deacon@....com>
Cc: Marcelo Tosatti <mtosatti@...hat.com>
Cc: Christian Borntraeger <borntraeger@...ibm.com>
Cc: Luiz Capitulino <lcapitulino@...hat.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Frederic Weisbecker <fweisbec@...il.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 17715d8..a2c0866 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 == CONTEXT_USER) {
+				trace_user_enter(0);
+				vtime_user_enter(current);
+			}
 			rcu_user_enter();
 		}
 		/*
@@ -143,8 +145,10 @@ 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 == CONTEXT_USER) {
+				vtime_user_exit(current);
+				trace_user_exit(0);
+			}
 		}
 		__this_cpu_write(context_tracking.state, CONTEXT_KERNEL);
 	}
-- 
2.1.4

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