linux-kernel - [RFC PATCH 10/11] nohz,kvm,time: skip vtime accounting at kernel entry & exit

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Date:	Wed, 24 Jun 2015 10:57:59 -0400
From:	riel@...hat.com
To:	linux-kernel@...r.kernel.org
Cc:	fweisbec@...hat.com, peterz@...radead.org, mingo@...nel.org,
	tglx@...utronix.de, luto@...capital.net
Subject: [RFC PATCH 10/11] nohz,kvm,time: skip vtime accounting at kernel entry & exit

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

When timer statistics are sampled from a remote CPU, vtime calculations
at the kernel/user and kernel/guest boundary are no longer necessary.
Skip them.

Signed-off-by: Rik van Riel <riel@...hat.com>
---
 include/linux/context_tracking.h | 4 ++--
 kernel/context_tracking.c        | 6 ++++--
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h
index d7ee7eb9e0bc..e3e7c674543f 100644
--- a/include/linux/context_tracking.h
+++ b/include/linux/context_tracking.h
@@ -90,7 +90,7 @@ static inline void context_tracking_init(void) { }
 #ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
 static inline void guest_enter(void)
 {
-	if (tick_accounting_disabled())
+	if (tick_accounting_disabled() && !tick_accounting_remote())
 		vtime_guest_enter(current);
 	else
 		current->flags |= PF_VCPU;
@@ -104,7 +104,7 @@ static inline void guest_exit(void)
 	if (context_tracking_is_enabled())
 		__context_tracking_exit(CONTEXT_GUEST);
 
-	if (tick_accounting_disabled())
+	if (tick_accounting_disabled() && !tick_accounting_remote())
 		vtime_guest_exit(current);
 	else
 		current->flags &= ~PF_VCPU;
diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
index 6da4205c3184..a58cbed13ebd 100644
--- a/kernel/context_tracking.c
+++ b/kernel/context_tracking.c
@@ -63,7 +63,8 @@ void __context_tracking_enter(enum ctx_state state)
 			 */
 			if (state == CONTEXT_USER) {
 				trace_user_enter(0);
-				vtime_user_enter(current);
+				if (!tick_accounting_remote())
+					vtime_user_enter(current);
 			}
 			rcu_user_enter();
 		}
@@ -135,7 +136,8 @@ void __context_tracking_exit(enum ctx_state state)
 			 */
 			rcu_user_exit();
 			if (state == CONTEXT_USER) {
-				vtime_user_exit(current);
+				if (!tick_accounting_remote())
+					vtime_user_exit(current);
 				trace_user_exit(0);
 			}
 		}
-- 
2.1.0

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