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

Andrew Morton
2008-10-30T20:39:56Z

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");
>