From owner-freebsd-toolchain@FreeBSD.ORG Tue Sep 11 14:42:15 2012 Return-Path: Delivered-To: toolchain@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id C50B31065670; Tue, 11 Sep 2012 14:42:15 +0000 (UTC) (envelope-from asmrookie@gmail.com) Received: from mail-lpp01m010-f54.google.com (mail-lpp01m010-f54.google.com [209.85.215.54]) by mx1.freebsd.org (Postfix) with ESMTP id E06098FC0C; Tue, 11 Sep 2012 14:42:14 +0000 (UTC) Received: by lage12 with SMTP id e12so463183lag.13 for ; Tue, 11 Sep 2012 07:42:13 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:reply-to:sender:in-reply-to:references:date :x-google-sender-auth:message-id:subject:from:to:cc:content-type; bh=ELF5BAbc6wSThC8KMFgTo0GKfqXRZymsmmQzn3IfMiY=; b=t8TBKFYaVdeUxds4KuVkuCEpnOHkvKMSi70SzUifRrtteLFCzn2B4aLJUMA2g0onJ4 B//e6O9cvZE2m0NEcxLy5KRBTlyP4wh3KVQtLgy97bRLMiWbMIg8ByYg8rp/80TSbtBn OfPMe0h07mjh9AsdThet+5sMBA48EV4ioTwxwp8rtP7smNykBHDYdDNCaRMbrg5Rw1j3 S6NINrs2deP7NjUUDvbWQZrQFRKK4dqdEVEXFItSxpZ2zkflV6PCkkpSGsrPkUmdnURd UUCiMDbVzLlgepoPXbE1/K9p3Q2ykZFyWjfcqmHzVXvHvySdhdAxvqVwXI3guwovV9Gr Dy8w== MIME-Version: 1.0 Received: by 10.152.131.68 with SMTP id ok4mr16080295lab.47.1347374533601; Tue, 11 Sep 2012 07:42:13 -0700 (PDT) Sender: asmrookie@gmail.com Received: by 10.112.102.39 with HTTP; Tue, 11 Sep 2012 07:42:13 -0700 (PDT) In-Reply-To: <20120911140825.GA73518@lor.one-eyed-alien.net> References: <20120910211207.GC64920@lor.one-eyed-alien.net> <20120911104518.GF37286@deviant.kiev.zoral.com.ua> <20120911140825.GA73518@lor.one-eyed-alien.net> Date: Tue, 11 Sep 2012 15:42:13 +0100 X-Google-Sender-Auth: YKj1fEkth4a17MqvNvyZdm6Iy6E Message-ID: From: Attilio Rao To: Brooks Davis Content-Type: text/plain; charset=UTF-8 Cc: toolchain@freebsd.org, current@freebsd.org Subject: Re: Clang as default compiler November 4th X-BeenThere: freebsd-toolchain@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list Reply-To: attilio@FreeBSD.org List-Id: Maintenance of FreeBSD's integrated toolchain List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 11 Sep 2012 14:42:15 -0000 On 9/11/12, Brooks Davis wrote: > On Tue, Sep 11, 2012 at 01:45:18PM +0300, Konstantin Belousov wrote: >> On Mon, Sep 10, 2012 at 04:12:07PM -0500, Brooks Davis wrote: >> > For the past several years we've been working towards migrating from >> > GCC to Clang/LLVM as our default compiler. We intend to ship FreeBSD >> > 10.0 with Clang as the default compiler on i386 and amd64 platforms. >> > To >> > this end, we will make WITH_CLANG_IS_CC the default on i386 and amd64 >> > platforms on November 4th. >> > >> > What does the mean to you? >> > >> > * When you build world after the default is changed /usr/bin/cc, cpp, >> > and >> > c++ will be links to clang. >> > >> > * This means the initial phase of buildworld and "old style" kernel >> > compilation will use clang instead of gcc. This is known to work. >> > >> > * It also means that ports will build with clang by default. A major >> > of ports work, but a significant number are broken or blocked by >> > broken ports. For more information see: >> > http://wiki.freebsd.org/PortsAndClang >> > >> > What issues remain? >> > >> > * The gcc->clang transition currently requires setting CC, CXX, and >> > CPP >> > in addition to WITH_CLANG_IS_CC. I will post a patch to toolchain@ >> > to address this shortly. >> > >> > * Ports compiler selection infrastructure is still under development. >> > >> > * Some ports could build with clang with appropriate tweaks. >> > >> > What can you do to help? >> > >> > * Switch (some of) your systems. Early adoption can help us find >> > bugs. >> > >> > * Fix ports to build with clang. If you don't have a clang system, >> > you >> > can use the CLANG/amd64 or CLANG/i386 build environments on >> > redports.org. >> > >> > tl;dr: Clang will become the default compiler for x86 architectures on >> > 2012-11-04 >> >> There was a chorus of voices talking about ports already. My POV >> is that suggesting to 'fix remaining ports to work with clang' is >> just a nonsense. You are proposing to fork the development of all the >> programs which do not compile with clang. Often, upstream developers >> do not care about clang at all since it not being default compiler in >> Debian/Fedora/Whatever Linux. The project simply do not have resources >> to maintain the fork of 20K programs. > > I may have phrased the above poorly, but in most cases I'd be happy with > using USE_GCC as a solution, but to the extent that port maintainers > can fix their ports to build with clang, that's a good thing. Having a > deadline will help focus efforts towards finding the right fix for the > most important ports in a timely manner. > > If we near the deadline and find that we need a few more weeks, nothing > prevents us from slipping the date a bit. > >> Another issue with the switch, which seems to be not only not addressed, >> but even not talked about, is the performance impact of the change. I >> do not remember any measurements, whatever silly they could be, of the >> performance change by the compiler switch. We often have serious and >> argumented push-back for kernel changes that give as low as 2-3% of >> the speed hit. What are the numbers for clang change, any numbers ? > > Florian Smeets (flo) did one round of benchmarks back in June with > sysbench/mysql. There is a small but measurable slowdown both with > world compiled with clang and with mysql compiled with clang. You can > see the results on the last page of this document: > > http://people.freebsd.org/~flo/perf.pdf > > The total impacts are on the order of 1-2%. That's more than I'd like > and I expect some pushback, but I feel it is in the range of acceptable > code debt to take on to accomplish a multi-year project goal. 1-2% on SMP workload can just be part of the variance due to memory layout changes. What I would like to see is benchmarks in UP configurations, like machine booting with only one process and doing make buildworld (no -j at all). This could give a good measurement if the compiler changed anything or not. Attilio -- Peace can only be achieved by understanding - A. Einstein