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authorSeiji Aguchi <seiji.aguchi@hds.com>2013-06-20 11:45:17 -0400
committerH. Peter Anvin <hpa@linux.intel.com>2013-06-20 22:25:01 -0700
commiteddc0e922a3530e0f22cef170229bcae3a7d5e31 (patch)
tree473c0c70cddcc8f8d23713c0bb65fcbf4dc9cd26 /arch/x86/include/asm/apic.h
parentf5abaa1bfc3dbf26d19d3513f39279ca369f8d65 (diff)
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>
Diffstat (limited to 'arch/x86/include/asm/apic.h')
-rw-r--r--arch/x86/include/asm/apic.h27
1 files changed, 27 insertions, 0 deletions
diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
index 33880342223..f8119b582c3 100644
--- a/arch/x86/include/asm/apic.h
+++ b/arch/x86/include/asm/apic.h
@@ -12,6 +12,7 @@
#include <asm/fixmap.h>
#include <asm/mpspec.h>
#include <asm/msr.h>
+#include <asm/idle.h>
#define ARCH_APICTIMER_STOPS_ON_C3 1
@@ -687,5 +688,31 @@ extern int default_check_phys_apicid_present(int phys_apicid);
#endif
#endif /* CONFIG_X86_LOCAL_APIC */
+extern void irq_enter(void);
+extern void irq_exit(void);
+
+static inline void entering_irq(void)
+{
+ irq_enter();
+ exit_idle();
+}
+
+static inline void entering_ack_irq(void)
+{
+ ack_APIC_irq();
+ entering_irq();
+}
+
+static inline void exiting_irq(void)
+{
+ irq_exit();
+}
+
+static inline void exiting_ack_irq(void)
+{
+ irq_exit();
+ /* Ack only at the end to avoid potential reentry */
+ ack_APIC_irq();
+}
#endif /* _ASM_X86_APIC_H */