From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755299AbbHDD6E (ORCPT ); Mon, 3 Aug 2015 23:58:04 -0400 Received: from smtprelay0079.hostedemail.com ([216.40.44.79]:52696 "EHLO smtprelay.hostedemail.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1755245AbbHDD6A (ORCPT ); Mon, 3 Aug 2015 23:58:00 -0400 X-Session-Marker: 6A6F6540706572636865732E636F6D X-Spam-Summary: 2,0,0,,d41d8cd98f00b204,joe@perches.com,:::::::::,RULES_HIT:41:355:379:541:599:973:988:989:1260:1277:1311:1313:1314:1345:1359:1373:1437:1515:1516:1518:1534:1541:1593:1594:1711:1730:1747:1777:1792:2393:2559:2562:2828:3138:3139:3140:3141:3142:3353:3622:3865:3866:3867:3868:3870:3871:3872:3874:4250:4321:4605:5007:6261:7875:8660:10004:10400:10848:11026:11232:11658:11914:12114:12296:12438:12517:12519:12740:13019:13069:13095:13148:13230:13311:13357:14096:14097:14346:21080,0,RBL:none,CacheIP:none,Bayesian:0.5,0.5,0.5,Netcheck:none,DomainCache:0,MSF:not bulk,SPF:fn,MSBL:0,DNSBL:none,Custom_rules:0:0:0 X-HE-Tag: love52_62afb7283780f X-Filterd-Recvd-Size: 2743 Message-ID: <1438660677.10829.1.camel@perches.com> Subject: Re: [PATCH] net_dbg_ratelimited: turn into no-op when !DEBUG From: Joe Perches To: "Jason A. Donenfeld" Cc: Andrew Morton , "David S. Miller" , netdev@vger.kernel.org, linux-kernel@vger.kernel.org Date: Mon, 03 Aug 2015 20:57:57 -0700 In-Reply-To: <1438658773-3220-1-git-send-email-Jason@zx2c4.com> References: <1438658773-3220-1-git-send-email-Jason@zx2c4.com> Content-Type: text/plain; charset="ISO-8859-1" X-Mailer: Evolution 3.12.11-0ubuntu3 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2015-08-04 at 05:26 +0200, Jason A. Donenfeld wrote: > The pr_debug family of functions turns into a no-op when -DDEBUG is not > specified, opting instead to call "no_printk", which gets compiled to a > no-op (but retains gcc's nice warnings about printf-style arguments). > > The problem with net_dbg_ratelimited is that it is defined to be a > variant of net_ratelimited_function, which expands to essentially: > > if (net_ratelimit()) > pr_debug(fmt, ...); > > When DEBUG is not defined, then this becomes, > > if (net_ratelimit()) > ; > > This seems benign, except it isn't. Firstly, there's the obvious > overhead of calling net_ratelimit needlessly, which does quite some book > keeping for the rate limiting. Given that the pr_debug and > net_dbg_ratelimited family of functions are sprinkled liberally through > performance critical code, with developers assuming they'll be compiled > out to a no-op most of the time, we certainly do not want this needless > book keeping. Secondly, and most visibly, even though no debug message > is printed when DEBUG is not defined, if there is a flood of > invocations, dmesg winds up peppered with messages such as > "net_ratelimit: 320 callbacks suppressed". This is because our > aforementioned net_ratelimit() function actually prints this text in > some circumstances. It's especially odd to see this when there isn't any > other accompanying debug message. > > So, in sum, it doesn't make sense to have this function's current > behavior, and instead it should match what every other debug family of > functions in the kernel does with !DEBUG -- nothing. > > This patch replaces calls to net_dbg_ratelimited when !DEBUG with > no_printk, keeping with the idiom of all the other debug print helpers. Makes sense, thanks Jason.