From eddc0e922a3530e0f22cef170229bcae3a7d5e31 Mon Sep 17 00:00:00 2001 From: Seiji Aguchi Date: Thu, 20 Jun 2013 11:45:17 -0400 Subject: 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 Link: http://lkml.kernel.org/r/51C3238D.9040706@hds.com Signed-off-by: H. Peter Anvin Cc: Steven Rostedt --- arch/x86/kernel/cpu/mcheck/threshold.c | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-) (limited to 'arch/x86/kernel/cpu/mcheck/threshold.c') diff --git a/arch/x86/kernel/cpu/mcheck/threshold.c b/arch/x86/kernel/cpu/mcheck/threshold.c index aa578cadb940..610cd98d6ef9 100644 --- a/arch/x86/kernel/cpu/mcheck/threshold.c +++ b/arch/x86/kernel/cpu/mcheck/threshold.c @@ -17,13 +17,15 @@ static void default_threshold_interrupt(void) void (*mce_threshold_vector)(void) = default_threshold_interrupt; -asmlinkage void smp_threshold_interrupt(void) +static inline void __smp_threshold_interrupt(void) { - irq_enter(); - exit_idle(); inc_irq_stat(irq_threshold_count); mce_threshold_vector(); - irq_exit(); - /* Ack only at the end to avoid potential reentry */ - ack_APIC_irq(); +} + +asmlinkage void smp_threshold_interrupt(void) +{ + entering_irq(); + __smp_threshold_interrupt(); + exiting_ack_irq(); } -- cgit v1.2.3