x86, bts, ftrace: a BTS ftrace plug-in prototype
Impact: add new ftrace plugin
A prototype for a BTS ftrace plug-in.
The tracer collects branch trace in a cyclic buffer for each cpu.
The tracer is not configurable and the trace for each snapshot is
appended when doing cat /debug/tracing/trace.
This is a proof of concept that will be extended with future patches
to become a (hopefully) useful tool.
Signed-off-by: Markus Metzger <markus.t.metzger@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/arch/x86/Kconfig.cpu b/arch/x86/Kconfig.cpu
index b815664..85a7857 100644
--- a/arch/x86/Kconfig.cpu
+++ b/arch/x86/Kconfig.cpu
@@ -515,6 +515,7 @@
config X86_DS
def_bool X86_PTRACE_BTS
depends on X86_DEBUGCTLMSR
+ select HAVE_HW_BRANCH_TRACER
config X86_PTRACE_BTS
bool "Branch Trace Store"
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 9cbf776..620fead 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -28,6 +28,9 @@
config HAVE_FTRACE_MCOUNT_RECORD
bool
+config HAVE_HW_BRANCH_TRACER
+ bool
+
config TRACER_MAX_TRACE
bool
@@ -233,6 +236,14 @@
Say N if unsure.
+config BTS_TRACER
+ depends on HAVE_HW_BRANCH_TRACER
+ bool "Trace branches"
+ select TRACING
+ help
+ This tracer records all branches on the system in a circular
+ buffer giving access to the last N branches for each cpu.
+
config DYNAMIC_FTRACE
bool "enable/disable ftrace tracepoints dynamically"
depends on FUNCTION_TRACER
diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
index 1a8c925..cef4bcb 100644
--- a/kernel/trace/Makefile
+++ b/kernel/trace/Makefile
@@ -31,5 +31,6 @@
obj-$(CONFIG_BOOT_TRACER) += trace_boot.o
obj-$(CONFIG_FUNCTION_RET_TRACER) += trace_functions_return.o
obj-$(CONFIG_TRACE_BRANCH_PROFILING) += trace_branch.o
+obj-$(CONFIG_BTS_TRACER) += trace_bts.o
libftrace-y := ftrace.o
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 717f9f0..3abd645 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -27,6 +27,7 @@
TRACE_BOOT_RET,
TRACE_FN_RET,
TRACE_USER_STACK,
+ TRACE_BTS,
__TRACE_LAST_TYPE
};
@@ -153,6 +154,12 @@
char correct;
};
+struct bts_entry {
+ struct trace_entry ent;
+ unsigned long from;
+ unsigned long to;
+};
+
/*
* trace_flag_type is an enumeration that holds different
* states when a trace occurs. These are:
@@ -258,6 +265,7 @@
IF_ASSIGN(var, ent, struct trace_boot_ret, TRACE_BOOT_RET);\
IF_ASSIGN(var, ent, struct trace_branch, TRACE_BRANCH); \
IF_ASSIGN(var, ent, struct ftrace_ret_entry, TRACE_FN_RET);\
+ IF_ASSIGN(var, ent, struct bts_entry, TRACE_BTS);\
__ftrace_bad_type(); \
} while (0)
@@ -392,6 +400,10 @@
void
trace_function_return(struct ftrace_retfunc *trace);
+void trace_bts(struct trace_array *tr,
+ unsigned long from,
+ unsigned long to);
+
void tracing_start_cmdline_record(void);
void tracing_stop_cmdline_record(void);
void tracing_sched_switch_assign_trace(struct trace_array *tr);
diff --git a/kernel/trace/trace_bts.c b/kernel/trace/trace_bts.c
new file mode 100644
index 0000000..23b76e4
--- /dev/null
+++ b/kernel/trace/trace_bts.c
@@ -0,0 +1,276 @@
+/*
+ * BTS tracer
+ *
+ * Copyright (C) 2008 Markus Metzger <markus.t.metzger@gmail.com>
+ *
+ */
+
+#include <linux/module.h>
+#include <linux/fs.h>
+#include <linux/debugfs.h>
+#include <linux/ftrace.h>
+#include <linux/kallsyms.h>
+
+#include <asm/ds.h>
+
+#include "trace.h"
+
+
+#define SIZEOF_BTS (1 << 13)
+
+static DEFINE_PER_CPU(struct bts_tracer *, tracer);
+static DEFINE_PER_CPU(unsigned char[SIZEOF_BTS], buffer);
+
+#define this_tracer per_cpu(tracer, smp_processor_id())
+#define this_buffer per_cpu(buffer, smp_processor_id())
+
+
+/*
+ * Information to interpret a BTS record.
+ * This will go into an in-kernel BTS interface.
+ */
+static unsigned char sizeof_field;
+static unsigned long debugctl_mask;
+
+#define sizeof_bts (3 * sizeof_field)
+
+static void bts_trace_cpuinit(struct cpuinfo_x86 *c)
+{
+ switch (c->x86) {
+ case 0x6:
+ switch (c->x86_model) {
+ case 0x0 ... 0xC:
+ break;
+ case 0xD:
+ case 0xE: /* Pentium M */
+ sizeof_field = sizeof(long);
+ debugctl_mask = (1<<6)|(1<<7);
+ break;
+ default:
+ sizeof_field = 8;
+ debugctl_mask = (1<<6)|(1<<7);
+ break;
+ }
+ break;
+ case 0xF:
+ switch (c->x86_model) {
+ case 0x0:
+ case 0x1:
+ case 0x2: /* Netburst */
+ sizeof_field = sizeof(long);
+ debugctl_mask = (1<<2)|(1<<3);
+ break;
+ default:
+ /* sorry, don't know about them */
+ break;
+ }
+ break;
+ default:
+ /* sorry, don't know about them */
+ break;
+ }
+}
+
+static inline void bts_enable(void)
+{
+ unsigned long debugctl;
+
+ rdmsrl(MSR_IA32_DEBUGCTLMSR, debugctl);
+ wrmsrl(MSR_IA32_DEBUGCTLMSR, debugctl | debugctl_mask);
+}
+
+static inline void bts_disable(void)
+{
+ unsigned long debugctl;
+
+ rdmsrl(MSR_IA32_DEBUGCTLMSR, debugctl);
+ wrmsrl(MSR_IA32_DEBUGCTLMSR, debugctl & ~debugctl_mask);
+}
+
+static void bts_trace_reset(struct trace_array *tr)
+{
+ int cpu;
+
+ tr->time_start = ftrace_now(tr->cpu);
+
+ for_each_online_cpu(cpu)
+ tracing_reset(tr, cpu);
+}
+
+static void bts_trace_start_cpu(void *arg)
+{
+ this_tracer =
+ ds_request_bts(/* task = */ NULL, this_buffer, SIZEOF_BTS,
+ /* ovfl = */ NULL, /* th = */ (size_t)-1);
+ if (IS_ERR(this_tracer)) {
+ this_tracer = NULL;
+ return;
+ }
+
+ bts_enable();
+}
+
+static void bts_trace_start(struct trace_array *tr)
+{
+ int cpu;
+
+ bts_trace_reset(tr);
+
+ for_each_cpu_mask(cpu, cpu_possible_map)
+ smp_call_function_single(cpu, bts_trace_start_cpu, NULL, 1);
+}
+
+static void bts_trace_stop_cpu(void *arg)
+{
+ if (this_tracer) {
+ bts_disable();
+
+ ds_release_bts(this_tracer);
+ this_tracer = NULL;
+ }
+}
+
+static void bts_trace_stop(struct trace_array *tr)
+{
+ int cpu;
+
+ for_each_cpu_mask(cpu, cpu_possible_map)
+ smp_call_function_single(cpu, bts_trace_stop_cpu, NULL, 1);
+}
+
+static int bts_trace_init(struct trace_array *tr)
+{
+ bts_trace_cpuinit(&boot_cpu_data);
+ bts_trace_reset(tr);
+ bts_trace_start(tr);
+
+ return 0;
+}
+
+static void bts_trace_print_header(struct seq_file *m)
+{
+#ifdef __i386__
+ seq_puts(m, "# CPU# FROM TO FUNCTION\n");
+ seq_puts(m, "# | | | |\n");
+#else
+ seq_puts(m,
+ "# CPU# FROM TO FUNCTION\n");
+ seq_puts(m,
+ "# | | | |\n");
+#endif
+}
+
+static enum print_line_t bts_trace_print_line(struct trace_iterator *iter)
+{
+ struct trace_entry *entry = iter->ent;
+ struct trace_seq *seq = &iter->seq;
+ struct bts_entry *it;
+
+ trace_assign_type(it, entry);
+
+ if (entry->type == TRACE_BTS) {
+ int ret;
+#ifdef CONFIG_KALLSYMS
+ char function[KSYM_SYMBOL_LEN];
+ sprint_symbol(function, it->from);
+#else
+ char *function = "<unknown>";
+#endif
+
+ ret = trace_seq_printf(seq, "%4d 0x%lx -> 0x%lx [%s]\n",
+ entry->cpu, it->from, it->to, function);
+ if (!ret)
+ return TRACE_TYPE_PARTIAL_LINE;;
+ return TRACE_TYPE_HANDLED;
+ }
+ return TRACE_TYPE_UNHANDLED;
+}
+
+void trace_bts(struct trace_array *tr, unsigned long from, unsigned long to)
+{
+ struct ring_buffer_event *event;
+ struct bts_entry *entry;
+ unsigned long irq;
+
+ event = ring_buffer_lock_reserve(tr->buffer, sizeof(*entry), &irq);
+ if (!event)
+ return;
+ entry = ring_buffer_event_data(event);
+ tracing_generic_entry_update(&entry->ent, 0, from);
+ entry->ent.type = TRACE_BTS;
+ entry->ent.cpu = smp_processor_id();
+ entry->from = from;
+ entry->to = to;
+ ring_buffer_unlock_commit(tr->buffer, event, irq);
+}
+
+static void trace_bts_at(struct trace_array *tr, size_t index)
+{
+ const void *raw = NULL;
+ unsigned long from, to;
+ int err;
+
+ err = ds_access_bts(this_tracer, index, &raw);
+ if (err < 0)
+ return;
+
+ from = *(const unsigned long *)raw;
+ to = *(const unsigned long *)((const char *)raw + sizeof_field);
+
+ trace_bts(tr, from, to);
+}
+
+static void trace_bts_cpu(void *arg)
+{
+ struct trace_array *tr = (struct trace_array *) arg;
+ size_t index = 0, end = 0, i;
+ int err;
+
+ if (!this_tracer)
+ return;
+
+ bts_disable();
+
+ err = ds_get_bts_index(this_tracer, &index);
+ if (err < 0)
+ goto out;
+
+ err = ds_get_bts_end(this_tracer, &end);
+ if (err < 0)
+ goto out;
+
+ for (i = index; i < end; i++)
+ trace_bts_at(tr, i);
+
+ for (i = 0; i < index; i++)
+ trace_bts_at(tr, i);
+
+out:
+ bts_enable();
+}
+
+static void trace_bts_prepare(struct trace_iterator *iter)
+{
+ int cpu;
+
+ for_each_cpu_mask(cpu, cpu_possible_map)
+ smp_call_function_single(cpu, trace_bts_cpu, iter->tr, 1);
+}
+
+struct tracer bts_tracer __read_mostly =
+{
+ .name = "bts",
+ .init = bts_trace_init,
+ .reset = bts_trace_stop,
+ .print_header = bts_trace_print_header,
+ .print_line = bts_trace_print_line,
+ .start = bts_trace_start,
+ .stop = bts_trace_stop,
+ .open = trace_bts_prepare
+};
+
+__init static int init_bts_trace(void)
+{
+ return register_tracer(&bts_tracer);
+}
+device_initcall(init_bts_trace);
