From owner-svn-src-head@FreeBSD.ORG Thu Dec 4 20:36:57 2014 Return-Path: Delivered-To: svn-src-head@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id E7AD7E0E; Thu, 4 Dec 2014 20:36:57 +0000 (UTC) Received: from mail.turbocat.net (heidi.turbocat.net [88.198.202.214]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id A670A72; Thu, 4 Dec 2014 20:36:57 +0000 (UTC) Received: from laptop015.home.selasky.org (cm-176.74.213.204.customer.telag.net [176.74.213.204]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.turbocat.net (Postfix) with ESMTPSA id AFACC1FE023; Thu, 4 Dec 2014 21:36:47 +0100 (CET) Message-ID: <5480C5FA.4030402@selasky.org> Date: Thu, 04 Dec 2014 21:37:14 +0100 From: Hans Petter Selasky User-Agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0 MIME-Version: 1.0 To: John-Mark Gurney Subject: Re: svn commit: r275468 - head/sys/dev/usb/controller References: <201412032155.sB3LtjJN043364@svn.freebsd.org> <20141204005451.GM99957@funkthat.com> <54800B60.9020208@selasky.org> <20141204175032.GQ99957@funkthat.com> In-Reply-To: <20141204175032.GQ99957@funkthat.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 04 Dec 2014 20:36:58 -0000 On 12/04/14 18:50, John-Mark Gurney wrote: > Hans Petter Selasky wrote this message on Thu, Dec 04, 2014 at 08:21 +0100: >> On 12/04/14 01:54, John-Mark Gurney wrote: >>> Hans Petter Selasky wrote this message on Wed, Dec 03, 2014 at 21:55 +0000: >>>> Author: hselasky >>>> Date: Wed Dec 3 21:55:44 2014 >>>> New Revision: 275468 >>>> URL: https://svnweb.freebsd.org/changeset/base/275468 >>>> >>>> Log: >>>> Optimise the bit searching loops, by quickly skipping the 16 first set >>>> bits if all the 16 first bits are set. This way the worst case >>>> searching time is reduced from 32 to 16 cycles. >>> >>> You could use ffs instead: >>> x = ffs(~map); >>> if (x) { >>> x--; >>> /* normal code */ >>> } >>> >>> This has the benefit of using a single instruction on platforms that >>> support it (bsfl on i386), though apparently, we haven't optimized this >>> for all platforms... arm has a version for int, but their ffsl does >>> the same linear search instead of just calling ffs, or at least >>> detecting if sizeof(long) == sizeof(int) and calling ffs... >>> >> >> Yes, I'm aware about that, but like you say it is not optimised for all >> platforms yet. So I'm not sure if it will give any benefit for the >> platform the driver is running on .... >> >> I'll see if I can change the logic inside the C-version of ffs() and the >> do the swap like you suggest. > > Did you see the comment about usig __builtin_ffs{,l,ll} instead? this > seems to be a better route... > Hi, I see. Who can update the cpufunc.h header file to use the builtins? Are these also available with GCC? --HPS