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context_tracking: avoid irq_save/irq_restore on guest entry and exit

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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@kernel.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Rik van Riel <riel@redhat.com>
Tested-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2015-10-28 02:39:56 +01:00
parent f70cd6b07e
commit d0e536d893
2 changed files with 44 additions and 28 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
include/linux/context_tracking.h
View File

@ -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);

64
kernel/context_tracking.c
View File

@ -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);