From owner-svn-src-all@FreeBSD.ORG Mon Feb 9 23:08:11 2015 Return-Path: Delivered-To: svn-src-all@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id 0FBFC174; Mon, 9 Feb 2015 23:08:11 +0000 (UTC) Received: from bigwig.baldwin.cx (bigwig.baldwin.cx [IPv6:2001:470:1f11:75::1]) (using TLSv1 with cipher DHE-RSA-CAMELLIA256-SHA (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id DB4DEE25; Mon, 9 Feb 2015 23:08:10 +0000 (UTC) Received: from ralph.baldwin.cx (pool-173-54-116-245.nwrknj.fios.verizon.net [173.54.116.245]) by bigwig.baldwin.cx (Postfix) with ESMTPSA id B466EB91E; Mon, 9 Feb 2015 18:08:09 -0500 (EST) From: John Baldwin To: Jung-uk Kim Subject: Re: svn commit: r278474 - head/sys/sys Date: Mon, 09 Feb 2015 18:08:02 -0500 Message-ID: <5703806.fFzzT9N1y2@ralph.baldwin.cx> User-Agent: KMail/4.14.2 (FreeBSD/10.1-STABLE; KDE/4.14.2; amd64; ; ) In-Reply-To: <54D93461.8010109@FreeBSD.org> References: <201502092103.t19L3OAn013792@svn.freebsd.org> <3501684.yzo0NMkRZd@ralph.baldwin.cx> <54D93461.8010109@FreeBSD.org> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.2.7 (bigwig.baldwin.cx); Mon, 09 Feb 2015 18:08:09 -0500 (EST) Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org X-BeenThere: svn-src-all@freebsd.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: "SVN commit messages for the entire src tree \(except for " user" and " projects" \)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 09 Feb 2015 23:08:11 -0000 On Monday, February 09, 2015 05:27:45 PM Jung-uk Kim wrote: > On 02/09/2015 17:12, John Baldwin wrote: > > On Monday, February 09, 2015 04:55:52 PM Jung-uk Kim wrote: > >> On 02/09/2015 16:08, John Baldwin wrote: > >>> On Monday, February 09, 2015 09:03:24 PM John Baldwin wrote: > >>>> Author: jhb Date: Mon Feb 9 21:03:23 2015 New Revision: > >>>> 278474 URL: https://svnweb.freebsd.org/changeset/base/278474 > >>>> > >>>> Log: Use __builtin_popcnt() to implement a BIT_COUNT() > >>>> operation for bitsets and use this to implement CPU_COUNT() > >>>> to count the number of CPUs in a cpuset. > >>>> > >>>> MFC after: 2 weeks > >>> > >>> Yes, __builtin_popcnt() works with GCC 4.2. It should also > >>> allow the compiler to DTRT in userland uses of this if -msse4.2 > >>> is enabled. > >> > >> Back in 2012, when I submitted a similar patch, bde noted > >> __builtin_popcount*() cannot be used with GCC 4.2 for *kernel* > >> because it emits a library call. > >> > >> http://docs.freebsd.org/cgi/mid.cgi?20121116171923.L1135 > >> > >> FYI... > > > > Weird, I though I built a kernel with this in a tree that uses it > > in the igb(4) driver. We need a CPU_COUNT() no matter what, but if > > this emits a library call under GCC I will need to add the call. > > We could also adopt your bitcount header, though I think it is more > > consistent to keep the loop in BIT_COUNT() and use something that > > emulates popcountl() rather than directly using bitcount() in > > BIT_COUNT() (primarily because the rest of sys/bitset.h is > > structured that way: explicit loops in sys/bitset.h itself). > > I think you should back it out for now and move the discussion to arch > or hackers. I gave it up at the time but you may have better luck. :-) > > FYI, the following was the last version of my patch at the time. > > https://people.freebsd.org/~jkim/bitcount5.diff I could also just make it userland only for now? Rui wants to use it in userland. However, I can back it out if that is preferred. To be honest, I'm not sure how valuable it is at this point to expend a lot of effort to support GCC older than 3.4 (i.e. the non-builtin popcount approach). -- John Baldwin