From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeff Garzik Subject: Re: [PATCH] ixgbe: Introduce new 10GbE driver for Intel 82598 based PCI Express adapters... Date: Mon, 02 Jul 2007 10:41:00 -0400 Message-ID: <46890E7C.9070204@garzik.org> References: <20070612234417.5102.29147.stgit@localhost.localdomain> <20070612234431.5102.33880.stgit@localhost.localdomain> <4688F512.3030801@garzik.org> <4689062A.8080809@linux.intel.com> <46890AED.7070906@garzik.org> <46890B39.4050909@linux.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: Ayyappan Veeraiyan , netdev@vger.kernel.org, auke-jan.h.kok@intel.com, akpm@linux-foundation.org To: Arjan van de Ven Return-path: Received: from srv5.dvmed.net ([207.36.208.214]:52236 "EHLO mail.dvmed.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755771AbXGBOlD (ORCPT ); Mon, 2 Jul 2007 10:41:03 -0400 In-Reply-To: <46890B39.4050909@linux.intel.com> Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org Arjan van de Ven wrote: > Jeff Garzik wrote: >>>> always avoid bitfields. They generate horrible code, and endian >>>> problems abound (though no endian problems are apparent here). >>> >>> they generate no worse code than open coding the checks for these >>> feature flags... >> >> That would be the logical assumption, but reality does not bear that >> logic out to be true. >> > > I just checked a small example and gcc just generates a testb with an > immediate value, which isn't all that bad code. > > Do you remember which gcc you tested with? gcc 2.95, gcc 3.x, gcc 4.x, ... on multiple architectures, not just ia32. It's simple logic: using machine integers are the easiest for the compiler to Do The Right Thing, the easiest way to eliminate endian problems, the easiest way for programmers to read and understand struct alignment. Just say no to bitfields. Jeff