From: Wu Zhangjin <wuzj@xxxxxxxxxx>
by default, ring_buffer_time_stamp calling sched_clock(jiffies-based)
function to get timestamp, in x86, there is a tsc(64bit) based
sched_clock, but in mips, the 'tsc'(clock counter) is only 32bit long,
which will easily rollover, and there is no precise sched_clock in mips,
we need to get one ourselves.
to avoid invading the whole linux-mips, i do not want to implement a
tsc-based native_sched_clock like x86 does. because, there is a need to
handling rollover of the only 32-bit long 'tsc' of mips, which will need
extra overhead. in reality, i have tried to implement one(just like the
ring_buffer_time_stamp here does), but make the kernel hangs when
booting, i am not sure why it not work.
herein, i just implement a mips-specific ring_buffer_time_stamp in
arch/mips/kernel/ftrace.c via adding __attribute__((weak)) before
ring_buffer_time_stamp(...) {} in kernel/trace/ring_buffer.c and do
something in arch/mips/kernel/ftrace.c like this:
u64 ring_buffer_time_stamp \
__attribute__((alias("native_ring_buffer_time_stamp")));
and, as the same, there is also a need to implement a mips-specific
trace_clock_local based on the above ring_buffer_timep_stamp, this clock
function is called in function graph tracer to get calltime & rettime of
a function.
and what about the trace_clock and trace_clock_global function, should
we also implement a mips-secific one? i am not sure.
Signed-off-by: Wu Zhangjin <wuzj@xxxxxxxxxx>
---
arch/mips/kernel/Makefile | 2 +
arch/mips/kernel/csrc-r4k.c | 2 +-
arch/mips/kernel/ftrace_clock.c | 77 +++++++++++++++++++++++++++++++++++++++
kernel/trace/ring_buffer.c | 3 +-
kernel/trace/trace_clock.c | 2 +-
5 files changed, 83 insertions(+), 3 deletions(-)
create mode 100644 arch/mips/kernel/ftrace_clock.c
diff --git a/arch/mips/kernel/Makefile b/arch/mips/kernel/Makefile
index 6b1a8a5..5dec76f 100644
--- a/arch/mips/kernel/Makefile
+++ b/arch/mips/kernel/Makefile
@@ -12,6 +12,7 @@ ifdef CONFIG_FUNCTION_TRACER
# Do not profile debug and lowlevel utilities
CFLAGS_REMOVE_mcount.o = -pg
CFLAGS_REMOVE_ftrace.o = -pg
+CFLAGS_REMOVE_ftrace_clock.o = -pg
CFLAGS_REMOVE_early_printk.o = -pg
endif
@@ -33,6 +34,7 @@ obj-$(CONFIG_MODULES) += mips_ksyms.o module.o
obj-$(CONFIG_FUNCTION_TRACER) += mcount.o
obj-$(CONFIG_FUNCTION_TRACER) += ftrace.o
+obj-$(CONFIG_NOP_TRACER) += ftrace_clock.o
obj-$(CONFIG_CPU_LOONGSON2) += r4k_fpu.o r4k_switch.o
obj-$(CONFIG_CPU_MIPS32) += r4k_fpu.o r4k_switch.o
diff --git a/arch/mips/kernel/csrc-r4k.c b/arch/mips/kernel/csrc-r4k.c
index e95a3cd..3da1c7a 100644
--- a/arch/mips/kernel/csrc-r4k.c
+++ b/arch/mips/kernel/csrc-r4k.c
@@ -10,7 +10,7 @@
#include <asm/time.h>
-static cycle_t c0_hpt_read(struct clocksource *cs)
+static cycle_t notrace c0_hpt_read(struct clocksource *cs)
{
return read_c0_count();
}
diff --git a/arch/mips/kernel/ftrace_clock.c b/arch/mips/kernel/ftrace_clock.c
new file mode 100644
index 0000000..2f3b05a
--- /dev/null
+++ b/arch/mips/kernel/ftrace_clock.c
@@ -0,0 +1,77 @@
+/*
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License. See the file "COPYING" in the main directory of this archive for
+ * more details.
+ *
+ * Copyright (C) 2009 DSLab, Lanzhou University, China
+ * Author: Wu Zhangjin <wuzj@xxxxxxxxxx>
+ */
+
+#include <linux/types.h>
+#include <linux/sched.h>
+#include <linux/jiffies.h>
+#include <linux/clocksource.h>
+#include <linux/ring_buffer.h>
+
+/* Up this if you want to test the TIME_EXTENTS and normalization */
+#ifndef DEBUG_SHIFT
+#define DEBUG_SHIFT 0
+#endif
+
+/* mips-specific ring_buffer_time_stamp implementation,
+ * the original one is defined in kernel/trace/ring_buffer.c
+ */
+
+u64 native_ring_buffer_time_stamp(struct ring_buffer *buffer, int cpu)
+{
+ u64 current_cycles;
+ static unsigned long old_jiffies;
+ static u64 time, old_cycles;
+
+ preempt_disable_notrace();
+ /* update timestamp to avoid missing the timer interrupt */
+ if (time_before(jiffies, old_jiffies)) {
+ old_jiffies = jiffies;
+ time = sched_clock();
+ old_cycles = clock->cycle_last;
+ }
+ current_cycles = clock->read(clock);
+
+ time = (time + cyc2ns(clock, (current_cycles - old_cycles)
+ & clock->mask)) << DEBUG_SHIFT;
+
+ old_cycles = current_cycles;
+ preempt_enable_no_resched_notrace();
+
+ return time;
+}
+
+u64 ring_buffer_time_stamp(struct ring_buffer *buffer, int cpu)
+ __attribute__((alias("native_ring_buffer_time_stamp")));
+
+/*
+ * native_trace_clock_local(): the simplest and least coherent tracing clock.
+ *
+ * Useful for tracing that does not cross to other CPUs nor
+ * does it go through idle events.
+ */
+u64 native_trace_clock_local(void)
+{
+ unsigned long flags;
+ u64 clock;
+
+ /*
+ * sched_clock() is an architecture implemented, fast, scalable,
+ * lockless clock. It is not guaranteed to be coherent across
+ * CPUs, nor across CPU idle events.
+ */
+ raw_local_irq_save(flags);
+ clock = ring_buffer_time_stamp(NULL, raw_smp_processor_id());
+ raw_local_irq_restore(flags);
+
+ return clock;
+}
+
+u64 trace_clock_local(void)
+ __attribute__((alias("native_trace_clock_local")));
+
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 960cbf4..717bd8e 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -420,7 +420,8 @@ struct ring_buffer_iter {
/* Up this if you want to test the TIME_EXTENTS and normalization */
#define DEBUG_SHIFT 0
-u64 ring_buffer_time_stamp(struct ring_buffer *buffer, int cpu)
+u64 __attribute__((weak)) ring_buffer_time_stamp(struct ring_buffer *buffer,
+ int cpu)
{
u64 time;
diff --git a/kernel/trace/trace_clock.c b/kernel/trace/trace_clock.c
index b588fd8..78c98c8 100644
--- a/kernel/trace/trace_clock.c
+++ b/kernel/trace/trace_clock.c
@@ -26,7 +26,7 @@
* Useful for tracing that does not cross to other CPUs nor
* does it go through idle events.
*/
-u64 notrace trace_clock_local(void)
+u64 __attribute__((weak)) notrace trace_clock_local(void)
{
unsigned long flags;
u64 clock;
--
1.6.0.4
