On Fri, 2009-10-16 at 19:38 +0800, Wu Zhangjin wrote:
> By default, trace_clock_local() call the sched_clock() to get timestamp,
> in x86, there is a tsc(64bit) based sched_clock(), but in MIPS, the
> sched_clock() is jiffies based, which can not give enough
> precision(about 10ms with 1000 HZ). so, we need to implement a higher
> precision version for MIPS.
>
> in MIPS, there is a tsc like clock counter. based on it, we can
> implement a new trace_clock_local(), but because the clock counter is
> only 32bit long, we need to handle rollover for it. fortunately, there
> a high-level abstraction(cyclecounter) of this action implemented in
> include/linux/clocksource.h, which helps to handle the details behind,
> we just use it!
>
> Signed-off-by: Wu Zhangjin <wuzhangjin@xxxxxxxxx>
> ---
> arch/mips/kernel/Makefile | 6 +++
> arch/mips/kernel/trace_clock.c | 67 ++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 73 insertions(+), 0 deletions(-)
> create mode 100644 arch/mips/kernel/trace_clock.c
>
> diff --git a/arch/mips/kernel/Makefile b/arch/mips/kernel/Makefile
> index 8e26e9c..f228868 100644
> --- a/arch/mips/kernel/Makefile
> +++ b/arch/mips/kernel/Makefile
> @@ -8,6 +8,10 @@ obj-y += cpu-probe.o branch.o entry.o genex.o irq.o process.o \
> ptrace.o reset.o setup.o signal.o syscall.o \
> time.o topology.o traps.o unaligned.o watch.o
>
> +ifdef CONFIG_FUNCTION_TRACER
> +CFLAGS_REMOVE_trace_clock.o = -pg
> +endif
> +
> obj-$(CONFIG_CEVT_BCM1480) += cevt-bcm1480.o
> obj-$(CONFIG_CEVT_R4K_LIB) += cevt-r4k.o
> obj-$(CONFIG_MIPS_MT_SMTC) += cevt-smtc.o
> @@ -24,6 +28,8 @@ obj-$(CONFIG_SYNC_R4K) += sync-r4k.o
> obj-$(CONFIG_STACKTRACE) += stacktrace.o
> obj-$(CONFIG_MODULES) += mips_ksyms.o module.o
>
> +obj-$(CONFIG_FTRACE) += trace_clock.o
> +
> obj-$(CONFIG_CPU_LOONGSON2) += r4k_fpu.o r4k_switch.o
> obj-$(CONFIG_CPU_MIPS32) += r4k_fpu.o r4k_switch.o
> obj-$(CONFIG_CPU_MIPS64) += r4k_fpu.o r4k_switch.o
> diff --git a/arch/mips/kernel/trace_clock.c b/arch/mips/kernel/trace_clock.c
> new file mode 100644
> index 0000000..435cd56
> --- /dev/null
> +++ b/arch/mips/kernel/trace_clock.c
> @@ -0,0 +1,67 @@
> +/*
> + * 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 Lemote Inc. & DSLab, Lanzhou University, China
> + * Author: Wu Zhangjin <wuzj@xxxxxxxxxx>
> + */
> +
> +#include <linux/clocksource.h>
> +#include <linux/sched.h>
> +
> +#include <asm/time.h>
> +
> +/*
> + * MIPS clock counter based timecounter.
> + */
> +
> +struct timecounter mips_tc;
> +
> +/*
> + * 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 trace_clock_local(void)
> +{
> + unsigned long flags;
> + u64 clock;
> +
> + raw_local_irq_save(flags);
> +
> + preempt_disable_notrace();
> +
> + clock = timecounter_read(&mips_tc);
> +
> + preempt_enable_no_resched_notrace();
> +
> + raw_local_irq_restore(flags);
> +
> + return clock;
> +}
> +
> +static cycle_t mips_cc_read(const struct cyclecounter *cc)
> +{
> + return read_c0_count();
> +}
> +
> +static struct cyclecounter mips_cc = {
> + .read = mips_cc_read,
> + .mask = CLOCKSOURCE_MASK(32),
> + .shift = 32,
> +};
> +
> +static int __init mips_timecounter_init(void)
> +{
> + uint64_t mips_freq = mips_hpt_frequency;
> +
we must ensure mips_hpt_frequency is initialized before using it.
> + mips_cc.mult = div_sc((unsigned long)mips_freq, NSEC_PER_SEC, 32);
> +
> + timecounter_init(&mips_tc, &mips_cc, sched_clock());
> +
> + return 0;
> +}
> +
> +arch_initcall(mips_timecounter_init);
mips_timecounter_init() must called before ftrace_init(), so can not put
it into *_initcall sections(which will be called in rest_init()).
Regards,
Wu Zhangjin
