linux-kernel - Re: [PATCH] ratelimit: check the condition in WARN

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Date:	Fri, 17 Aug 2012 11:45:39 -0700
From:	Joe Perches <joe@...ches.com>
To:	Jiri Slaby <jslaby@...e.cz>
Cc:	davem@...emloft.net, jirislaby@...il.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ratelimit: check the condition in WARN_RATELIMIT first

On Fri, 2012-08-17 at 20:15 +0200, Jiri Slaby wrote:
> On 08/17/2012 07:39 PM, Joe Perches wrote:
> > On Fri, 2012-08-17 at 15:42 +0200, Jiri Slaby wrote:
> >> Before calling __ratelimit in __WARN_RATELIMIT, check the condition
> >> first. When this check was not there, we got constant income of:
> >> tty_init_dev: 60 callbacks suppressed
> >> tty_init_dev: 59 callbacks suppressed
> > []
> >> diff --git a/include/linux/ratelimit.h b/include/linux/ratelimit.h
> > []
> >> @@ -49,8 +49,9 @@ extern int ___ratelimit(struct ratelimit_state *rs, const char *func);
> >>  #define __WARN_RATELIMIT(condition, state, format...)		\
> >>  ({								\
> >>  	int rtn = 0;						\
> >> -	if (unlikely(__ratelimit(state)))			\
> >> -		rtn = WARN(condition, format);			\
> >> +	int __rtcond = !!condition;				\
> >> +	if (unlikely(__rtcond && __ratelimit(state)))		\
> >> +		rtn = WARN(__rtcond, format);			\
> >>  	rtn;							\
> >>  })
> >>  
> > 
> > Hi Jiri.
> > 
> > This seems fine to me but are there any conditions that
> > are computationally expensive?
> 
> It's not about expensiveness of the computation. The complexity remained
> the same except I moved the computation one layer up.

If ratelimit(state) is not true, condition wasn't tested
or performed at all.  With this change, it's always done.

> > Maybe something like this?
[]
> Yup, something like that looks OK to me.

OK, David, do you want an official patch?


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