linux-kernel - Re: [PATCH] Sound USB: Prevent printk ratelimiting from spamming kernel log while DEBUG not defined

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Date:	Fri, 02 May 2014 18:13:09 +0200
From:	Takashi Iwai <tiwai@...e.de>
To:	Sander Eikelenboom <linux@...elenboom.it>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Julia Lawall <julia.lawall@...6.fr>,
	linux-sound@...r.kernel.org,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Sound USB: Prevent printk ratelimiting from spamming kernel log while DEBUG not defined

At Fri,  2 May 2014 15:09:27 +0200,
Sander Eikelenboom wrote:
> 
> This (widely used) construction:
> 
> if(printk_ratelimit())
> 	dev_dbg()
> 
> Causes the ratelimiting to spam the kernel log with the "callbacks suppressed"
> message below, even while the dev_dbg it is supposed to rate limit wouldn't
> print anything because DEBUG is not defined for this device.
> 
> [  533.803964] retire_playback_urb: 852 callbacks suppressed
> [  538.807930] retire_playback_urb: 852 callbacks suppressed
> [  543.811897] retire_playback_urb: 852 callbacks suppressed
> [  548.815745] retire_playback_urb: 852 callbacks suppressed
> [  553.819826] retire_playback_urb: 852 callbacks suppressed
> 
> So use dev_dbg_ratelimited() instead of this construction.
> 
> Signed-off-by: Sander Eikelenboom <linux@...elenboom.it>

Thanks, applied.  This is a result of the recent rewrite to dev_dbg()
from plain printk(), I suppose.


Takashi

> ---
>  sound/usb/pcm.c |    5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c
> index 131336d..c62a165 100644
> --- a/sound/usb/pcm.c
> +++ b/sound/usb/pcm.c
> @@ -1501,9 +1501,8 @@ static void retire_playback_urb(struct snd_usb_substream *subs,
>  	 * The error should be lower than 2ms since the estimate relies
>  	 * on two reads of a counter updated every ms.
>  	 */
> -	if (printk_ratelimit() &&
> -	    abs(est_delay - subs->last_delay) * 1000 > runtime->rate * 2)
> -		dev_dbg(&subs->dev->dev,
> +	if (abs(est_delay - subs->last_delay) * 1000 > runtime->rate * 2)
> +		dev_dbg_ratelimited(&subs->dev->dev,
>  			"delay: estimated %d, actual %d\n",
>  			est_delay, subs->last_delay);
>  
> -- 
> 1.7.10.4
> 
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