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linux/arch/x86/kernel/tracepoint.c

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x86, trace: Add irq vector tracepoints [Purpose of this patch] As Vaibhav explained in the thread below, tracepoints for irq vectors are useful. http://www.spinics.net/lists/mm-commits/msg85707.html <snip> The current interrupt traces from irq_handler_entry and irq_handler_exit provide when an interrupt is handled. They provide good data about when the system has switched to kernel space and how it affects the currently running processes. There are some IRQ vectors which trigger the system into kernel space, which are not handled in generic IRQ handlers. Tracing such events gives us the information about IRQ interaction with other system events. The trace also tells where the system is spending its time. We want to know which cores are handling interrupts and how they are affecting other processes in the system. Also, the trace provides information about when the cores are idle and which interrupts are changing that state. <snip> On the other hand, my usecase is tracing just local timer event and getting a value of instruction pointer. I suggested to add an argument local timer event to get instruction pointer before. But there is another way to get it with external module like systemtap. So, I don't need to add any argument to irq vector tracepoints now. [Patch Description] Vaibhav's patch shared a trace point ,irq_vector_entry/irq_vector_exit, in all events. But there is an above use case to trace specific irq_vector rather than tracing all events. In this case, we are concerned about overhead due to unwanted events. So, add following tracepoints instead of introducing irq_vector_entry/exit. so that we can enable them independently. - local_timer_vector - reschedule_vector - call_function_vector - call_function_single_vector - irq_work_entry_vector - error_apic_vector - thermal_apic_vector - threshold_apic_vector - spurious_apic_vector - x86_platform_ipi_vector Also, introduce a logic switching IDT at enabling/disabling time so that a time penalty makes a zero when tracepoints are disabled. Detailed explanations are as follows. - Create trace irq handlers with entering_irq()/exiting_irq(). - Create a new IDT, trace_idt_table, at boot time by adding a logic to _set_gate(). It is just a copy of original idt table. - Register the new handlers for tracpoints to the new IDT by introducing macros to alloc_intr_gate() called at registering time of irq_vector handlers. - Add checking, whether irq vector tracing is on/off, into load_current_idt(). This has to be done below debug checking for these reasons. - Switching to debug IDT may be kicked while tracing is enabled. - On the other hands, switching to trace IDT is kicked only when debugging is disabled. In addition, the new IDT is created only when CONFIG_TRACING is enabled to avoid being used for other purposes. Signed-off-by: Seiji Aguchi <seiji.aguchi@hds.com> Link: http://lkml.kernel.org/r/51C323ED.5050708@hds.com Signed-off-by: H. Peter Anvin <hpa@linux.intel.com> Cc: Steven Rostedt <rostedt@goodmis.org>
2013-06-20 17:46:53 +02:00
/*
* Code for supporting irq vector tracepoints.
*
* Copyright (C) 2013 Seiji Aguchi <seiji.aguchi@hds.com>
*
*/
#include <asm/hw_irq.h>
#include <asm/desc.h>
#include <linux/atomic.h>
atomic_t trace_idt_ctr = ATOMIC_INIT(0);
struct desc_ptr trace_idt_descr = { NR_VECTORS * 16 - 1,
(unsigned long) trace_idt_table };
#ifndef CONFIG_X86_64
gate_desc trace_idt_table[NR_VECTORS] __page_aligned_data
= { { { { 0, 0 } } }, };
#endif
static int trace_irq_vector_refcount;
static DEFINE_MUTEX(irq_vector_mutex);
static void set_trace_idt_ctr(int val)
{
atomic_set(&trace_idt_ctr, val);
/* Ensure the trace_idt_ctr is set before sending IPI */
wmb();
}
static void switch_idt(void *arg)
{
load_current_idt();
}
void trace_irq_vector_regfunc(void)
{
mutex_lock(&irq_vector_mutex);
if (!trace_irq_vector_refcount) {
set_trace_idt_ctr(1);
smp_call_function(switch_idt, NULL, 0);
switch_idt(NULL);
}
trace_irq_vector_refcount++;
mutex_unlock(&irq_vector_mutex);
}
void trace_irq_vector_unregfunc(void)
{
mutex_lock(&irq_vector_mutex);
trace_irq_vector_refcount--;
if (!trace_irq_vector_refcount) {
set_trace_idt_ctr(0);
smp_call_function(switch_idt, NULL, 0);
switch_idt(NULL);
}
mutex_unlock(&irq_vector_mutex);
}