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Re: [PATCH -v4 3/9] tracing: add MIPS specific trace_clock_local()

To: Wu Zhangjin <wuzhangjin@gmail.com>
Subject: Re: [PATCH -v4 3/9] tracing: add MIPS specific trace_clock_local()
From: Steven Rostedt <rostedt@goodmis.org>
Date: Wed, 21 Oct 2009 10:46:33 -0400
Cc: linux-kernel@vger.kernel.org, linux-mips@linux-mips.org, Thomas Gleixner <tglx@linutronix.de>, Ralf Baechle <ralf@linux-mips.org>, Nicholas Mc Guire <der.herr@hofr.at>
In-reply-to: <3f0d3515f74a58f4cfd11e61b62a129fdc21e3a7.1256135456.git.wuzhangjin@gmail.com>
Organization: Kihon Technologies Inc.
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <028867b99ec532b84963a35e7d552becc783cafc.1256135456.git.wuzhangjin@gmail.com> <2f73eae542c47ac5bbb9f7280e6c0271d193e90d.1256135456.git.wuzhangjin@gmail.com> <3f0d3515f74a58f4cfd11e61b62a129fdc21e3a7.1256135456.git.wuzhangjin@gmail.com>
Reply-to: rostedt@goodmis.org
Sender: linux-mips-bounce@linux-mips.org
On Wed, 2009-10-21 at 22:34 +0800, Wu Zhangjin wrote:
> This patch add the mips_timecounter_read() based high precision version
> of trace_clock_local().
> 
> Signed-off-by: Wu Zhangjin <wuzhangjin@gmail.com>
> ---
>  arch/mips/kernel/Makefile      |    6 ++++++
>  arch/mips/kernel/trace_clock.c |   37 +++++++++++++++++++++++++++++++++++++
>  2 files changed, 43 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..2e3475f
> --- /dev/null
> +++ b/arch/mips/kernel/trace_clock.c
> @@ -0,0 +1,37 @@
> +/*
> + * 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@lemote.com>
> + */
> +
> +#include <linux/clocksource.h>
> +#include <linux/sched.h>
> +
> +#include <asm/time.h>
> +
> +/*
> + * 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();

Why have the preempt_disable? You disable interrupts already, that will
prevent any preemption at that point.

-- Steve

> +
> +     clock = mips_timecounter_read();
> +
> +     preempt_enable_no_resched_notrace();
> +
> +     raw_local_irq_restore(flags);
> +
> +     return clock;
> +}


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