linux-kernel - Re: [PATCH 1/2] dyndbg: avoid calling dyndbg_emit

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Message-ID: <f2e4773e-45a2-c4cb-24cb-fc8119f10a3a@akamai.com>
Date:   Thu, 29 Apr 2021 17:03:40 -0400
From:   Jason Baron <jbaron@...mai.com>
To:     Jim Cromie <jim.cromie@...il.com>, gregkh@...uxfoundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] dyndbg: avoid calling dyndbg_emit_prefix when it has
 no work

Hi Jim,

On 4/27/21 9:00 PM, Jim Cromie wrote:
> Wrap function in a static-inline one, which checks flags to avoid
> calling the function unnecessarily.
> 
> Signed-off-by: Jim Cromie <jim.cromie@...il.com>
> ---
>  include/linux/dynamic_debug.h | 9 +++++++++
>  lib/dynamic_debug.c           | 9 ++++++++-
>  2 files changed, 17 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/dynamic_debug.h b/include/linux/dynamic_debug.h
> index a57ee75342cf..173535e725f7 100644
> --- a/include/linux/dynamic_debug.h
> +++ b/include/linux/dynamic_debug.h
> @@ -32,6 +32,15 @@ struct _ddebug {
>  #define _DPRINTK_FLAGS_INCL_FUNCNAME	(1<<2)
>  #define _DPRINTK_FLAGS_INCL_LINENO	(1<<3)
>  #define _DPRINTK_FLAGS_INCL_TID		(1<<4)
> +
> +#define _DPRINTK_FLAGS_INCL_ANYSITE		\
> +	(_DPRINTK_FLAGS_INCL_MODNAME		\
> +	 | _DPRINTK_FLAGS_INCL_FUNCNAME		\
> +	 | _DPRINTK_FLAGS_INCL_LINENO)
> +#define _DPRINTK_FLAGS_INCL_ANY			\
> +	(_DPRINTK_FLAGS_INCL_ANYSITE		\
> +	 | _DPRINTK_FLAGS_INCL_TID)
> +

I'm not sure it's worth having an unused define here by dynamic_debug.c.

I would prefer to just have _DPRINTK_FLAGS_INCL_ANY that has all the flags
in a single define.

>  #if defined DEBUG
>  #define _DPRINTK_FLAGS_DEFAULT _DPRINTK_FLAGS_PRINT
>  #else
> diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
> index c70d6347afa2..613293896e47 100644
> --- a/lib/dynamic_debug.c
> +++ b/lib/dynamic_debug.c
> @@ -586,7 +586,7 @@ static int remaining(int wrote)
>  	return 0;
>  }
>  
> -static char *dynamic_emit_prefix(const struct _ddebug *desc, char *buf)
> +static char *__dynamic_emit_prefix(const struct _ddebug *desc, char *buf)
>  {
>  	int pos_after_tid;
>  	int pos = 0;
> @@ -618,6 +618,13 @@ static char *dynamic_emit_prefix(const struct _ddebug *desc, char *buf)
>  	return buf;
>  }
>  
> +static inline char *dynamic_emit_prefix(struct _ddebug *desc, char *buf)
> +{
> +	if (unlikely(desc->flags & _DPRINTK_FLAGS_INCL_ANY))
> +		return __dynamic_emit_prefix(desc, buf);
> +	return buf;
> +}
> +

hmmm - looking at __dynamic_emit_prefix() it starts by doing:


 589 static char *dynamic_emit_prefix(const struct _ddebug *desc, char *buf)
 590 {
 591         int pos_after_tid;
 592         int pos = 0;
 593
 594         *buf = '\0';


So now we are missing the string termination if no flags are set...

Thanks,

-Jason

>  void __dynamic_pr_debug(struct _ddebug *descriptor, const char *fmt, ...)
>  {
>  	va_list args;
>