linux-kernel - Re: [PATCH 1/1] ftrace: fix dynamic ftrace filter reset issue

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Message-ID: <1332531400.23924.71.camel@gandalf.stny.rr.com>
Date:	Fri, 23 Mar 2012 15:36:40 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Rajesh Bhagat <rajesh.lnx@...il.com>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] ftrace: fix dynamic ftrace filter reset issue

On Wed, 2012-03-21 at 11:22 +0530, Rajesh Bhagat wrote:
> >From 60ec8a88ba671fa0b424f7b4467dba3ea8a2a2c8 Mon Sep 17 00:00:00 2001
> From: Rajesh Bhagat <rajesh.lnx@...il.com>
> Date: Tue, 20 Mar 2012 10:35:59 +0530
> Subject: [PATCH 1/1] ftrace: fix dynamic ftrace filter reset issue
> 
> This patch resets the trace_array using tracing_reset_online_cpus, if same
> tracer is set again instead of just returning from funtion tracing_set_tracer.
> 
> problem description
> -------------------
> once function tracer is set, set_ftrace_filter not working.
> /debug/tracing # echo function > current_tracer
> /debug/tracing # echo schedule > set_ftrace_filter
> /debug/tracing # echo function > current_tracer

Sorry no. The correct way you want to do this is:

/debug/tracing # echo > trace

That will reset the buffer for you and give you the desired result.

-- Steve



> /debug/tracing #  cat trace
> # tracer: function
> #
> #           TASK-PID    CPU#    TIMESTAMP  FUNCTION
> #              | |       |          |         |
>           <idle>-0     [000]    21.997778: irq_enter <-handle_IRQ
>           <idle>-0     [000]    21.997785: idle_cpu <-irq_enter
>           <idle>-0     [000]    21.997794: local_bh_disable <-irq_enter
>           <idle>-0     [000]    21.997800: tick_check_idle <-irq_enter
>           <idle>-0     [000]    21.997807:
> tick_check_oneshot_broadcast <-tick_check_idle
>           <idle>-0     [000]    21.997814: _local_bh_enable <-irq_enter
> 
> After applying this patch, only filtered functions are traced.
> 
> Signed-off-by: Rajesh Bhagat <rajesh.lnx@...il.com>
> ---
>  kernel/trace/trace.c |    4 +++-
>  1 files changed, 3 insertions(+), 1 deletions(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index a3f1bc5..f4fb190 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -3058,8 +3058,10 @@ static int tracing_set_tracer(const char *buf)
>         ret = -EINVAL;
>         goto out;
>     }
> -   if (t == current_trace)
> +   if (t == current_trace) {
> +       tracing_reset_online_cpus(tr);
>         goto out;
> +   }
> 
>     trace_branch_disable();
>     if (current_trace && current_trace->reset)


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