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Message-ID: <alpine.DEB.2.00.0905282204060.11238@gandalf.stny.rr.com>
Date: Thu, 28 May 2009 22:06:42 -0400 (EDT)
From: Steven Rostedt <rostedt@...dmis.org>
To: wuzhangjin@...il.com
cc: linux-mips@...ux-mips.org, linux-kernel@...r.kernel.org,
Wu Zhangjin <wuzj@...ote.com>,
Ralf Baechle <ralf@...ux-mips.org>,
Ingo Molnar <mingo@...e.hu>,
Andrew Morton <akpm@...ux-foundation.org>,
Thomas Gleixner <tglx@...utronix.de>,
Nicholas Mc Guire <der.herr@...r.at>
Subject: Re: [PATCH v1 4/5] mips specific clock function to get precise
timestamp
On Fri, 29 May 2009, wuzhangjin@...il.com wrote:
> From: Wu Zhangjin <wuzj@...ote.com>
>
> 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@...ote.com>
> ---
> 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@...ote.com>
> + */
> +
> +#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)
> {
Note, you want to look at what is in tip:
http://people.redhat.com/~mingo/tip.git/README
The latest ftrace code is there. I changed the ring_buffer_time_stamp to
use an individule buffer clock, that defaults to trace_clock_local.
Then only the trace_clock_local needs to be weak.
-- Steve
> 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
>
>
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