From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752774AbcD1PtX (ORCPT ); Thu, 28 Apr 2016 11:49:23 -0400 Received: from mail-db3on0093.outbound.protection.outlook.com ([157.55.234.93]:32016 "EHLO emea01-db3-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752327AbcD1PtV (ORCPT ); Thu, 28 Apr 2016 11:49:21 -0400 Authentication-Results: ucw.cz; dkim=none (message not signed) header.d=none;ucw.cz; dmarc=none action=none header.from=mellanox.com; Subject: Re: [PATCH] scsi: fc: force inlining of wwn conversion functions To: Arnd Bergmann References: <20160419085221.GA29087@gmail.com> <4940273.pi2bWg8tAl@wuerfel> <2544325.pieyAoijz1@wuerfel> CC: Martin Jambor , "Martin K. Petersen" , James Bottomley , Josh Poimboeuf , , , Denys Vlasenko , Thomas Graf , Peter Zijlstra , David Rientjes , Andrew Morton , Ingo Molnar , Himanshu Madhani , , Jan Hubicka From: Chris Metcalf Message-ID: <744a7126-47f7-c325-b208-cab8c30bcc0d@mellanox.com> Date: Thu, 28 Apr 2016 11:48:57 -0400 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.0 MIME-Version: 1.0 In-Reply-To: <2544325.pieyAoijz1@wuerfel> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [12.216.194.146] X-ClientProxiedBy: BLUPR0201CA0040.namprd02.prod.outlook.com (10.163.116.50) To HE1PR05MB1692.eurprd05.prod.outlook.com (10.169.119.158) X-MS-Office365-Filtering-Correlation-Id: 20f51d7c-fa42-437e-462a-08d36f7ca706 X-Microsoft-Exchange-Diagnostics: 1;HE1PR05MB1692;2:4qq1Tx8H2Uh54fzC57pZPJiS7S977AZ0pjzNT0XVqmdg+ZhKSYuVq6bB1yZuCLzJSagtDGa8fVQl/JjVJ+XJx+I6FUk2uQEDRAbYAiocTPTg7MIVPKW7DMjbLdF2sHFfOFthi9BLwitNVf75y2iRMsf2i4qj5jmXb1uqwT3zmHQ1Wilpxq7SNqx6Jq2QyJRJ;3:hqZpifbslOhTfHpCqjI+UrIJWj8t85bgPtZgeTg3XELfcY5gfHC3TFYaetGuK5DEsqIr8TTCpnGaythrEwE+gmXUEjr7DmHUBeiq0XK1W5OzAstSaoLy2WmMRbknoH00 X-Microsoft-Antispam: UriScan:;BCL:0;PCL:0;RULEID:;SRVR:HE1PR05MB1692; 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The only problem is >> that we never added explicit support for bswap16() in gcc, which is >> efficiently done on tilegx via the "revbytes" instruction and a 48-bit >> right-shift. So gcc instead does a generic thing with four >> instructions in three bundles, so really not as good as our asm/swab.h. >> >> I'm not sure how to weigh the implications of converting to >> builtin_bswap16 (and possibly upstreaming a better implementation to >> gcc), vs. disabling ARCH_SUPPORTS_OPTIMIZED_INLINING (which no one >> else but x86 uses anyway), vs. just ignoring the compiler bug and >> hoping it's not an issue in practice > How about figuring out whether you hit the gcc bug on tile as a > first step? I don't have an affected build of gcc handy (just 4.8 and 4.4). I will pass this to our compiler folks and see what they know. > Another idea would be to adapt this section in include/linux/compiler-gcc.h: > > #if !defined(CONFIG_ARCH_SUPPORTS_OPTIMIZED_INLINING) || \ > !defined(CONFIG_OPTIMIZE_INLINING) || (__GNUC__ < 4) > #define inline inline __attribute__((always_inline)) notrace > #define __inline__ __inline__ __attribute__((always_inline)) notrace > #define __inline __inline __attribute__((always_inline)) notrace > #else > /* A lot of inline functions can cause havoc with function tracing */ > #define inline inline notrace > #define __inline__ __inline__ notrace > #define __inline __inline notrace > #endif > > to work around the issue. We already check for gcc before 4.0, and > we could also check for the affected releases (4.9, 5.x, 6.1) in the > same place, possibly conditional on ARCH_USE_BUILTIN_BSWAP with > a comment pointing to the gcc bug tracker. This does seem like a more robust solution anyway, since more instances of the bad inline pattern might get introduced in the future in other places. I wouldn't make it conditional on ARCH_USE_BUILTIN_BSWAP for the same reason. -- Chris Metcalf, Mellanox Technologies http://www.mellanox.com