Re: [PATCH 2/2] ftrace: nmi update statistics

[Andrew Morton <akpm@linux-foundation.org>]

On Thu, 30 Oct 2008 16:08:33 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> This patch adds dynamic ftrace NMI update statistics to the
> /debugfs/tracing/dyn_ftrace_total_info stat file.
> 
> Signed-off-by: Steven Rostedt <srostedt@redhat.com>
> ---
>  arch/x86/kernel/ftrace.c |   26 ++++++++++++++++++++++++--
>  kernel/trace/trace.c     |   31 ++++++++++++++++++++++++-------

No header files were modified, but ftrace_arch_read_dyn_info() should
have been declared so that the above two compilation units see the
declaration.

> 
> Index: linux-tip.git/arch/x86/kernel/ftrace.c
> ===================================================================
> --- linux-tip.git.orig/arch/x86/kernel/ftrace.c	2008-10-30 15:30:12.000000000 -0400
> +++ linux-tip.git/arch/x86/kernel/ftrace.c	2008-10-30 15:51:51.000000000 -0400
> @@ -91,6 +91,19 @@ static int mod_code_write;
>  static void *mod_code_ip;
>  static void *mod_code_newcode;
>  
> +static int nmi_wait_count;
> +static atomic_t nmi_update_count;

<the ATOMIC_INIT thing>

> +int ftrace_arch_read_dyn_info(char *buf, int size)
> +{
> +	int r;
> +
> +	r = snprintf(buf, size, "%u %u",
> +		     nmi_wait_count,
> +		     atomic_read(&nmi_update_count));
> +	return r;
> +}

Yes, nmi_wait_count is an unsigned quantity.  Might as well define it
thusly?

>  static void ftrace_mod_code(void)
>  {
>  	/*
> @@ -109,8 +122,10 @@ void ftrace_nmi_enter(void)
>  	atomic_inc(&in_nmi);
>  	/* Must have in_nmi seen before reading write flag */
>  	smp_mb();
> -	if (mod_code_write)
> +	if (mod_code_write) {
>  		ftrace_mod_code();
> +		atomic_inc(&nmi_update_count);
> +	}
>  }
>  
>  void ftrace_nmi_exit(void)
> @@ -122,8 +137,15 @@ void ftrace_nmi_exit(void)
>  
>  static void wait_for_nmi(void)
>  {
> -	while (atomic_read(&in_nmi))
> +	int waited = 0;
> +
> +	while (atomic_read(&in_nmi)) {
> +		waited = 1;
>  		cpu_relax();
> +	}
> +
> +	if (waited)
> +		nmi_wait_count++;
>  }
>  
>  static int
> Index: linux-tip.git/kernel/trace/trace.c
> ===================================================================
> --- linux-tip.git.orig/kernel/trace/trace.c	2008-10-30 15:18:45.000000000 -0400
> +++ linux-tip.git/kernel/trace/trace.c	2008-10-30 15:51:51.000000000 -0400
> @@ -2837,22 +2837,39 @@ static struct file_operations tracing_ma
>  
>  #ifdef CONFIG_DYNAMIC_FTRACE
>  
> +#define DYN_INFO_BUF_SIZE 1023
> +static char ftrace_dyn_info_buffer[DYN_INFO_BUF_SIZE+1];

Could be made local to tracing_read_dyn_info().


Could just be

	static char ftrace_dyn_info_buffer[1024];

then use sizeof/ARRAY_SIZE elsewhere.  I think this is a bit safer and
more readable - the reader doesn't have to run around the code checking
that the correct #define was used in both places.

> +static DEFINE_MUTEX(dyn_info_mutex);
> +
> +int __weak ftrace_arch_read_dyn_info(char *buf, int size)
> +{
> +	return 0;
> +}
> +
>  static ssize_t
> -tracing_read_long(struct file *filp, char __user *ubuf,
> +tracing_read_dyn_info(struct file *filp, char __user *ubuf,
>  		  size_t cnt, loff_t *ppos)
>  {
>  	unsigned long *p = filp->private_data;
> -	char buf[64];
> +	char *buf = ftrace_dyn_info_buffer;
>  	int r;
>  
> -	r = sprintf(buf, "%ld\n", *p);
> +	mutex_lock(&dyn_info_mutex);
> +	r = sprintf(buf, "%ld ", *p);
> +
> +	r += ftrace_arch_read_dyn_info(buf+r, DYN_INFO_BUF_SIZE-r);
> +	buf[r++] = '\n';
> +
> +	r = simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
> +
> +	mutex_unlock(&dyn_info_mutex);
>  
> -	return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
> +	return r;
>  }
>  
> -static struct file_operations tracing_read_long_fops = {
> +static struct file_operations tracing_dyn_info_fops = {
>  	.open		= tracing_open_generic,
> -	.read		= tracing_read_long,
> +	.read		= tracing_read_dyn_info,
>  };
>  #endif
>  
> @@ -2961,7 +2978,7 @@ static __init int tracer_init_debugfs(vo
>  #ifdef CONFIG_DYNAMIC_FTRACE
>  	entry = debugfs_create_file("dyn_ftrace_total_info", 0444, d_tracer,
>  				    &ftrace_update_tot_cnt,
> -				    &tracing_read_long_fops);
> +				    &tracing_dyn_info_fops);
>  	if (!entry)
>  		pr_warning("Could not create debugfs "
>  			   "'dyn_ftrace_total_info' entry\n");
>