From owner-freebsd-threads@FreeBSD.ORG Mon Mar 29 14:16:29 2004 Return-Path: Delivered-To: freebsd-threads@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id A8D0816A4CE for ; Mon, 29 Mar 2004 14:16:29 -0800 (PST) Received: from herring.rabson.org (mailgate.nlsystems.com [80.177.232.242]) by mx1.FreeBSD.org (Postfix) with ESMTP id C9ED643D3F for ; Mon, 29 Mar 2004 14:16:28 -0800 (PST) (envelope-from dfr@nlsystems.com) Received: from herring.rabson.org (herring.rabson.org [10.0.0.2]) by herring.rabson.org (8.12.11/8.12.11) with ESMTP id i2TMGHrR012354; Mon, 29 Mar 2004 23:16:17 +0100 (BST) (envelope-from dfr@nlsystems.com) From: Doug Rabson To: Daniel Eischen Date: Mon, 29 Mar 2004 23:16:17 +0100 User-Agent: KMail/1.6.1 References: In-Reply-To: MIME-Version: 1.0 Content-Disposition: inline Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <200403292316.17288.dfr@nlsystems.com> X-Spam-Status: No, hits=0.0 required=5.0 tests=none autolearn=no version=2.63 X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on herring.rabson.org X-Virus-Scanned: ClamAV version 'clamd / ClamAV version 0.65', clamav-milter version '0.60p' cc: freebsd-threads@freebsd.org Subject: Re: Thread Local Storage X-BeenThere: freebsd-threads@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Threading on FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 29 Mar 2004 22:16:29 -0000 On Monday 29 March 2004 22:56, Daniel Eischen wrote: > On Mon, 29 Mar 2004, Doug Rabson wrote: > > On Monday 29 March 2004 22:26, Daniel Eischen wrote: > > > On Mon, 29 Mar 2004, Doug Rabson wrote: > > > > Surely the GNU TLS ABI is preferable? It generates much smaller > > > > code and needs many fewer relocations. > > > > > > No, we don't want an LDT for every thread and don't want > > > to force a syscall for a thread switch. > > > > But the code it generates is at least twice the size for dynamic > > TLS. It seems that the GNU people have done a better job defining > > the TLS abi for i386. > > About the only thing that uses TLS that I know is nvidia's > openGL. If you design an API correctly, there's no need > for TLS. I would hope that it's usage would be limited. I'd quite like to see us use it for stuff like errno, _res and other uglification currently in libc. Not until the 6.x timeframe though. > > > You don't need a syscall at thread switch if you do something like: > > > > _thread_switch(...) > > { > > if (tcb doesn't have LDT entry) { > > if (!free LDT entries) > > steal LDT entry from non-running thread; > > allocate LDT entry and point it at TLS goop for tcb. > > } > > load_gs(tcb's LDT sel); > > That's a system call on amd64. I'm not quite up to speed on amd64. So in 64-bit mode it doesn't really have an LDT at all, is that right?