Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030823AbcCQM57 (ORCPT ); Thu, 17 Mar 2016 08:57:59 -0400 Received: from mx2.suse.de ([195.135.220.15]:34237 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1030651AbcCQM5z (ORCPT ); Thu, 17 Mar 2016 08:57:55 -0400 Subject: Re: [PATCH] scsi: fc: use get/put_unaligned64 for wwn access To: Arnd Bergmann , "James E.J. Bottomley" , "Martin K. Petersen" References: <1458146385-278589-1-git-send-email-arnd@arndb.de> Cc: James Bottomley , James Smart , "Ewan D. Milne" , linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org From: Hannes Reinecke Message-ID: <56EAA9CF.4000309@suse.de> Date: Thu, 17 Mar 2016 13:57:51 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0 MIME-Version: 1.0 In-Reply-To: <1458146385-278589-1-git-send-email-arnd@arndb.de> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1612 Lines: 42 On 03/16/2016 05:39 PM, Arnd Bergmann wrote: > A bug in the gcc-6.0 prerelease version caused at least one > driver (lpfc) to have excessive stack usage when dealing with > wwn data, on the ARM architecture. > > lpfc_scsi.c: In function 'lpfc_find_next_oas_lun': > lpfc_scsi.c:117:1: warning: the frame size of 1152 bytes is larger than 1024 bytes [-Wframe-larger-than=] > > I have reported this as a gcc regression in > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70232 > > However, using a better implementation of wwn_to_u64() not only > helps with the particular gcc problem but also leads to better > object code for any version or architecture. > > The kernel already provides get_unaligned_be64() and > put_unaligned_be64() helper functions that provide an > optimized implementation with the desired semantics. > > The lpfc_find_next_oas_lun() function in the example that > grew from 1146 bytes to 5144 bytes when moving from gcc-5.3 > to gcc-6.0 is now 804 bytes, as the optimized > get_unaligned_be64() load can be done in three instructions. > The stack usage is now down to 28 bytes from 128 bytes with > gcc-5.3 before. > > Signed-off-by: Arnd Bergmann > --- > include/scsi/scsi_transport_fc.h | 15 +++------------ > 1 file changed, 3 insertions(+), 12 deletions(-) > Reviewed-by: Hannes Reinecke Cheers, Hannes -- Dr. Hannes Reinecke Teamlead Storage & Networking hare@suse.de +49 911 74053 688 SUSE LINUX GmbH, Maxfeldstr. 5, 90409 N?rnberg GF: F. Imend?rffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton HRB 21284 (AG N?rnberg)