From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758759Ab2HQSPS (ORCPT ); Fri, 17 Aug 2012 14:15:18 -0400 Received: from mail-we0-f174.google.com ([74.125.82.174]:53441 "EHLO mail-we0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758645Ab2HQSPN (ORCPT ); Fri, 17 Aug 2012 14:15:13 -0400 Message-ID: <502E8A2C.3060606@suse.cz> Date: Fri, 17 Aug 2012 20:15:08 +0200 From: Jiri Slaby User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:15.0) Gecko/20120731 Thunderbird/15.0 MIME-Version: 1.0 To: Joe Perches CC: davem@davemloft.net, jirislaby@gmail.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH] ratelimit: check the condition in WARN_RATELIMIT first References: <1345210942-26906-1-git-send-email-jslaby@suse.cz> <1345225144.10014.2.camel@joe2Laptop> In-Reply-To: <1345225144.10014.2.camel@joe2Laptop> X-Enigmail-Version: 1.5a1pre Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. > ratelimit(state) isn't > and this will now always do condition. > > (looks instead of speculates) > > There's 1 current use of WARN_RATELIMIT and there's > a condition of 1 so there's no problem here. There is going to be one more in monday's -next. I've just added one to the TTY code. The thing is that when you call ratelimit(state) it will emit how many times you have called that function like I described in the changelog: tty_init_dev: 60 callbacks suppressed Even when the condition is always false. Hence I added the condition to the if and lazy evaluation will take care and ratelimit() won't be called at all... > __WARN_RATELIMIT is pretty stupid. > It's only called from WARN_RATELIMIT. > I think it shouldn't exist at all. > > Maybe something like this? Yup, something like that looks OK to me. thanks, -- js suse labs