From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: [PATCH] qede: fix CONFIG_INFINIBAND_QEDR=m build error Date: Thu, 13 Oct 2016 12:50:01 +0200 Message-ID: <42891984.bIYIOYDk0K@wuerfel> References: <20161012103340.978726-1-arnd@arndb.de> <5662883.yo8OytxU65@wuerfel> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7Bit Cc: Ariel Elior , "everest-linux-l2@qlogic.com" , Alexander Duyck , "Amrani, Ram" , "netdev@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "David S. Miller" To: "Mintz, Yuval" Return-path: Received: from mout.kundenserver.de ([212.227.126.134]:58069 "EHLO mout.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752940AbcJMKwl (ORCPT ); Thu, 13 Oct 2016 06:52:41 -0400 In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: On Thursday, October 13, 2016 10:44:36 AM CEST Mintz, Yuval wrote: > > > > > While I don't mind, you could have argued is that we're not > > > > > removing enough, not too much. > > > > > I.e., perhaps the rdma_msix_* fields should also have been > > > > > ifdef-ed instead. [in which case this solution would not have > > > > > worked] > > > > > > > > That would add even more #ifdefs though. > > > > > > I agree. Although I'm never clear on the guidelines for the tradeoff - > > > How much memory/code is considered too much so that you'd have To > > > ifdef code out instead of 'wasting'? > > > [I obviously don't claim 64 bytes of memory hit that threshold] > > > > I don't think code size should ever be a reason for an #ifdef in a .c > > file: if the code is well-structured, you can always get the same object code > > using if(IS_ENABLED()) checks within the code at better readability or better > > compile-time coverage. > > > > Between if(IS_ENABLED()) checks and inline helpers, it usually doesn't matter > > much either way as long as the separation between the modules is clear enough. > > In the example above, removing the structure fields however would require to > > move the debugging output into another inline function though. > > Still, the question remains - If we were to allocate X bytes of memory > per-something [in this case, per qed owned PCI function], and that memory > wouldn't be functional without a some CONFIG option enabled, > how big should X become before we'd decide the fields should also be > dependent on the option? > It bears no real relevance to this case, as the fields involved are > insignificantly small. But still - is there a rule of thumb here? I don't think there is a good general rule for that, given the vastly different memory sizes in machines. For a tiny embedded machine with 2MB of RAM, saving one kilobyte is very significant, while an any machine that uses a 500KB qed driver module probably has many gigabytes of RAM and doesn't care much about a a wasted megabyte. Arnd