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Date: Wed, 28 Oct 2015 02:39:56 +0100
From: Paolo Bonzini <pbonzini@...hat.com>
To: linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc: Andy Lutomirski <luto@...nel.org>,
Frederic Weisbecker <fweisbec@...il.com>,
Rik van Riel <riel@...hat.com>,
Paul McKenney <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH 2/3] context_tracking: avoid irq_save/irq_restore on guest entry and exit
guest_enter and guest_exit must be called with interrupts disabled,
since they take the vtime_seqlock with write_seq{lock,unlock}.
Therefore, it is not necessary to check for exceptions, nor to
save/restore the IRQ state, when context tracking functions are
called by guest_enter and guest_exit.
Split the body of context_tracking_entry and context_tracking_exit
out to __-prefixed functions, and use them from KVM.
Rik van Riel has measured this to speed up a tight vmentry/vmexit
loop by about 2%.
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: Rik van Riel <riel@...hat.com>
Cc: Paul McKenney <paulmck@...ux.vnet.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
include/linux/context_tracking.h | 8 +++--
kernel/context_tracking.c | 64 ++++++++++++++++++++++++----------------
2 files changed, 44 insertions(+), 28 deletions(-)
diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h
index 6ef136ff0897..68b575afe5f5 100644
--- a/include/linux/context_tracking.h
+++ b/include/linux/context_tracking.h
@@ -10,6 +10,10 @@
#ifdef CONFIG_CONTEXT_TRACKING
extern void context_tracking_cpu_set(int cpu);
+/* Called with interrupts disabled. */
+extern void __context_tracking_enter(enum ctx_state state);
+extern void __context_tracking_exit(enum ctx_state state);
+
extern void context_tracking_enter(enum ctx_state state);
extern void context_tracking_exit(enum ctx_state state);
extern void context_tracking_user_enter(void);
@@ -88,13 +92,13 @@ static inline void guest_enter(void)
current->flags |= PF_VCPU;
if (context_tracking_is_enabled())
- context_tracking_enter(CONTEXT_GUEST);
+ __context_tracking_enter(CONTEXT_GUEST);
}
static inline void guest_exit(void)
{
if (context_tracking_is_enabled())
- context_tracking_exit(CONTEXT_GUEST);
+ __context_tracking_exit(CONTEXT_GUEST);
if (vtime_accounting_enabled())
vtime_guest_exit(current);
diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
index 6d4c6ce21275..d8560ee3bab7 100644
--- a/kernel/context_tracking.c
+++ b/kernel/context_tracking.c
@@ -58,27 +58,13 @@ static void context_tracking_recursion_exit(void)
* instructions to execute won't use any RCU read side critical section
* because this function sets RCU in extended quiescent state.
*/
-void context_tracking_enter(enum ctx_state state)
+void __context_tracking_enter(enum ctx_state state)
{
- unsigned long flags;
-
- /*
- * Some contexts may involve an exception occuring in an irq,
- * leading to that nesting:
- * rcu_irq_enter() rcu_user_exit() rcu_user_exit() rcu_irq_exit()
- * This would mess up the dyntick_nesting count though. And rcu_irq_*()
- * helpers are enough to protect RCU uses inside the exception. So
- * just return immediately if we detect we are in an IRQ.
- */
- if (in_interrupt())
- return;
-
/* Kernel threads aren't supposed to go to userspace */
WARN_ON_ONCE(!current->mm);
- local_irq_save(flags);
if (!context_tracking_recursion_enter())
- goto out_irq_restore;
+ return;
if ( __this_cpu_read(context_tracking.state) != state) {
if (__this_cpu_read(context_tracking.active)) {
@@ -111,7 +97,27 @@ void context_tracking_enter(enum ctx_state state)
__this_cpu_write(context_tracking.state, state);
}
context_tracking_recursion_exit();
-out_irq_restore:
+}
+NOKPROBE_SYMBOL(__context_tracking_enter);
+EXPORT_SYMBOL_GPL(__context_tracking_enter);
+
+void context_tracking_enter(enum ctx_state state)
+{
+ unsigned long flags;
+
+ /*
+ * Some contexts may involve an exception occuring in an irq,
+ * leading to that nesting:
+ * rcu_irq_enter() rcu_user_exit() rcu_user_exit() rcu_irq_exit()
+ * This would mess up the dyntick_nesting count though. And rcu_irq_*()
+ * helpers are enough to protect RCU uses inside the exception. So
+ * just return immediately if we detect we are in an IRQ.
+ */
+ if (in_interrupt())
+ return;
+
+ local_irq_save(flags);
+ __context_tracking_enter(state);
local_irq_restore(flags);
}
NOKPROBE_SYMBOL(context_tracking_enter);
@@ -135,16 +141,10 @@ NOKPROBE_SYMBOL(context_tracking_user_enter);
* This call supports re-entrancy. This way it can be called from any exception
* handler without needing to know if we came from userspace or not.
*/
-void context_tracking_exit(enum ctx_state state)
+void __context_tracking_exit(enum ctx_state state)
{
- unsigned long flags;
-
- if (in_interrupt())
- return;
-
- local_irq_save(flags);
if (!context_tracking_recursion_enter())
- goto out_irq_restore;
+ return;
if (__this_cpu_read(context_tracking.state) == state) {
if (__this_cpu_read(context_tracking.active)) {
@@ -161,7 +161,19 @@ void context_tracking_exit(enum ctx_state state)
__this_cpu_write(context_tracking.state, CONTEXT_KERNEL);
}
context_tracking_recursion_exit();
-out_irq_restore:
+}
+NOKPROBE_SYMBOL(__context_tracking_exit);
+EXPORT_SYMBOL_GPL(__context_tracking_exit);
+
+void context_tracking_exit(enum ctx_state state)
+{
+ unsigned long flags;
+
+ if (in_interrupt())
+ return;
+
+ local_irq_save(flags);
+ __context_tracking_exit(state);
local_irq_restore(flags);
}
NOKPROBE_SYMBOL(context_tracking_exit);
--
2.5.0
--
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