From owner-svn-src-all@FreeBSD.ORG Wed Sep 30 13:49:00 2009 Return-Path: Delivered-To: svn-src-all@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 692F5106568B; Wed, 30 Sep 2009 13:49:00 +0000 (UTC) (envelope-from asmrookie@gmail.com) Received: from mail-bw0-f227.google.com (mail-bw0-f227.google.com [209.85.218.227]) by mx1.freebsd.org (Postfix) with ESMTP id 6848E8FC15; Wed, 30 Sep 2009 13:48:58 +0000 (UTC) Received: by bwz27 with SMTP id 27so4634963bwz.43 for ; Wed, 30 Sep 2009 06:48:58 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:sender:received:in-reply-to :references:date:x-google-sender-auth:message-id:subject:from:to:cc :content-type; bh=7kazmk04fOpNSms37kRlBHUJkwskBUYNMvu6RRLjWFw=; b=mUlkVTWN9Glh+DdXSFuhLhZKBOu7iN+uiTnJNWyP4t8Xtbh198JFGPHphZDIUIJhR8 cDsP8OVwX7eRxLWyUdfnmFc4k+fcXnodNt96R+MXgJ8rNYdV1W6WpA1bRhtNMJyenfRb fuPwa8kqmorXgA/ioIq6/kC2+XM/vH2smKm1I= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:sender:in-reply-to:references:date :x-google-sender-auth:message-id:subject:from:to:cc:content-type; b=rhU2ewYeixVdnZEpuLyOrNwUVqfzdwTpurn2W8SlM9rX4NFNJ4zaUU8PpA92cdD0lU XEPGMyfOKkNqKTQFPOIM6s4IiKu31WaAtNRIQySutNOFGsIJb041NpMxrnlmboAq057/ 57aPgZJQ1LlZJbNJ43X3DNYW2y1ShnePTeDw0= MIME-Version: 1.0 Sender: asmrookie@gmail.com Received: by 10.223.62.146 with SMTP id x18mr1752576fah.48.1254318538008; Wed, 30 Sep 2009 06:48:58 -0700 (PDT) In-Reply-To: <9bbcef730909300643k56e40be9xc8b8287dc2971ac3@mail.gmail.com> References: <200909301326.n8UDQVB1016396@svn.freebsd.org> <9bbcef730909300643k56e40be9xc8b8287dc2971ac3@mail.gmail.com> Date: Wed, 30 Sep 2009 15:48:57 +0200 X-Google-Sender-Auth: d9ea16cf538e80ee Message-ID: <3bbf2fe10909300648v51555353p864dd9682ecd884b@mail.gmail.com> From: Attilio Rao To: Ivan Voras Content-Type: text/plain; charset=UTF-8 Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r197643 - in head/sys: kern sys X-BeenThere: svn-src-all@freebsd.org X-Mailman-Version: 2.1.5 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: Wed, 30 Sep 2009 13:49:00 -0000 2009/9/30 Ivan Voras : > 2009/9/30 Attilio Rao : >> Author: attilio >> Date: Wed Sep 30 13:26:31 2009 >> New Revision: 197643 >> URL: http://svn.freebsd.org/changeset/base/197643 >> >> Log: >> When releasing a read/shared lock we need to use a write memory barrier >> in order to avoid, on architectures which doesn't have strong ordered >> writes, CPU instructions reordering. > > Will this influence performance on those architecture that do? > No. In those architectures, memory barriers are crafted in the lighter possible way (aka often are the same operation as a 'simple' atomic, like the ia32 case). Attilio -- Peace can only be achieved by understanding - A. Einstein