x86, trace: Introduce entering/exiting_irq()

When implementing tracepoints in interrupt handers, if the tracepoints are
simply added in the performance sensitive path of interrupt handers,
it may cause potential performance problem due to the time penalty.

To solve the problem, an idea is to prepare non-trace/trace irq handers and
switch their IDTs at the enabling/disabling time.

So, let's introduce entering_irq()/exiting_irq() for pre/post-
processing of each irq handler.

A way to use them is as follows.

Non-trace irq handler:
smp_irq_handler()
{
	entering_irq();		/* pre-processing of this handler */
	__smp_irq_handler();	/*
				 * common logic between non-trace and trace handlers
				 * in a vector.
				 */
	exiting_irq();		/* post-processing of this handler */

}

Trace irq_handler:
smp_trace_irq_handler()
{
	entering_irq();		/* pre-processing of this handler */
	trace_irq_entry();	/* tracepoint for irq entry */
	__smp_irq_handler();	/*
				 * common logic between non-trace and trace handlers
				 * in a vector.
				 */
	trace_irq_exit();	/* tracepoint for irq exit */
	exiting_irq();		/* post-processing of this handler */

}

If tracepoints can place outside entering_irq()/exiting_irq() as follows,
it looks cleaner.

smp_trace_irq_handler()
{
	trace_irq_entry();
	smp_irq_handler();
	trace_irq_exit();
}

But it doesn't work.
The problem is with irq_enter/exit() being called. They must be called before
trace_irq_enter/exit(),  because of the rcu_irq_enter() must be called before
any tracepoints are used, as tracepoints use  rcu to synchronize.

As a possible alternative, we may be able to call irq_enter() first as follows
if irq_enter() can nest.

smp_trace_irq_hander()
{
	irq_entry();
	trace_irq_entry();
	smp_irq_handler();
	trace_irq_exit();
	irq_exit();
}

But it doesn't work, either.
If irq_enter() is nested, it may have a time penalty because it has to check if it
was already called or not. The time penalty is not desired in performance sensitive
paths even if it is tiny.

Signed-off-by: Seiji Aguchi <seiji.aguchi@hds.com>
Link: http://lkml.kernel.org/r/51C3238D.9040706@hds.com
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Cc: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 19 insertions, 14 deletions

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index 904611bf0e5a..59ee76fe1c53 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -919,17 +919,14 @@ void __irq_entry smp_apic_timer_interrupt(struct pt_regs *regs)
 	/*
 	 * NOTE! We'd better ACK the irq immediately,
 	 * because timer handling can be slow.
-	 */
-	ack_APIC_irq();
-	/*
+	 *
 	 * update_process_times() expects us to have done irq_enter().
 	 * Besides, if we don't timer interrupts ignore the global
 	 * interrupt lock, which is the WrongThing (tm) to do.
 	 */
-	irq_enter();
-	exit_idle();
+	entering_ack_irq();
 	local_apic_timer_interrupt();
-	irq_exit();
+	exiting_irq();
 
 	set_irq_regs(old_regs);
 }
@@ -1907,12 +1904,10 @@ int __init APIC_init_uniprocessor(void)
 /*
  * This interrupt should _never_ happen with our APIC/SMP architecture
  */
-void smp_spurious_interrupt(struct pt_regs *regs)
+static inline void __smp_spurious_interrupt(void)
 {
 	u32 v;
 
-	irq_enter();
-	exit_idle();
 	/*
 	 * Check if this really is a spurious interrupt and ACK it
 	 * if it is a vectored one.  Just in case...
@@ -1927,13 +1922,19 @@ void smp_spurious_interrupt(struct pt_regs *regs)
 	/* see sw-dev-man vol 3, chapter 7.4.13.5 */
 	pr_info("spurious APIC interrupt on CPU#%d, "
 		"should never happen.\n", smp_processor_id());
-	irq_exit();
+}
+
+void smp_spurious_interrupt(struct pt_regs *regs)
+{
+	entering_irq();
+	__smp_spurious_interrupt();
+	exiting_irq();
 }
 
 /*
  * This interrupt should never happen with our APIC/SMP architecture
  */
-void smp_error_interrupt(struct pt_regs *regs)
+static inline void __smp_error_interrupt(struct pt_regs *regs)
 {
 	u32 v0, v1;
 	u32 i = 0;
@@ -1948,8 +1949,6 @@ void smp_error_interrupt(struct pt_regs *regs)
 		"Illegal register address",	/* APIC Error Bit 7 */
 	};
 
-	irq_enter();
-	exit_idle();
 	/* First tickle the hardware, only then report what went on. -- REW */
 	v0 = apic_read(APIC_ESR);
 	apic_write(APIC_ESR, 0);
@@ -1970,7 +1969,13 @@ void smp_error_interrupt(struct pt_regs *regs)
 
 	apic_printk(APIC_DEBUG, KERN_CONT "\n");
 
-	irq_exit();
+}
+
+void smp_error_interrupt(struct pt_regs *regs)
+{
+	entering_irq();
+	__smp_error_interrupt(regs);
+	exiting_irq();
 }
 
 /**