Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932551AbbHXIbW (ORCPT ); Mon, 24 Aug 2015 04:31:22 -0400 Received: from mail-pd0-f172.google.com ([209.85.192.172]:32950 "EHLO mail-pd0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753904AbbHXIbU convert rfc822-to-8bit (ORCPT ); Mon, 24 Aug 2015 04:31:20 -0400 Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 8.2 \(2104\)) Subject: Re: [RFC] fbdev/riva:change to use generice function to implement reverse_order() From: yalin wang In-Reply-To: <20150822075310.GA2337@afzalpc> Date: Mon, 24 Aug 2015 16:31:13 +0800 Cc: Tomi Valkeinen , adaplas@gmail.com, plagnioj@jcrosoft.com, linux-fbdev@vger.kernel.org, open list Content-Transfer-Encoding: 8BIT Message-Id: References: <55D5B3A9.6040901@ti.com> <867D66CD-9A3B-4536-B537-8C065C85E497@gmail.com> <55D6C812.6080400@ti.com> <4DCC50F3-9B6D-4A3A-9693-E7A7196564A8@gmail.com> <55D6DAE5.20304@ti.com> <20150822075310.GA2337@afzalpc> To: Afzal Mohammed X-Mailer: Apple Mail (2.2104) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1419 Lines: 39 > On Aug 22, 2015, at 15:53, Afzal Mohammed wrote: > > Hi, > > On Fri, Aug 21, 2015 at 11:01:41AM +0300, Tomi Valkeinen wrote: > >>>> Possibly the patches are still good for x86 also, but that needs to be >>>> proven. >>>> >>> not exactly, because x86_64 don’t have hardware instruction to do rbit OP, >>> i compile by test : >> >> For old drivers i386 may be more relevant than x86_64. > > It seems asm bit reversal is supported in Kernel on arm & arm64 only, > not sure whether any other arch even provide asm bit reversal > instruction. i only submit the bit reverse patch for arm / arm64 arch, i am not sure if there are some other arch also have hard ware bit reverse instructions, need arch maintainers to submit if their arch also have these hard ware instructions . :) > >> These kind of optimizations should have some real world measurements, > > Not for this case, but once measured on ARM, iirc, a 32-bit asm bit > reversal as compared to doing it in C was taking 1 cycle as opposed to > ~225 cycles!, of course writing optimized C could have made it fare > better, but still would reach no-way near asm bit reversal. > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/