From owner-freebsd-questions@FreeBSD.ORG Mon Aug 29 19:55:11 2011 Return-Path: Delivered-To: questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id F1705106564A for ; Mon, 29 Aug 2011 19:55:11 +0000 (UTC) (envelope-from bruce@cran.org.uk) Received: from muon.cran.org.uk (muon.cran.org.uk [IPv6:2a01:348:0:15:5d59:5c40:0:1]) by mx1.freebsd.org (Postfix) with ESMTP id 77D058FC14 for ; Mon, 29 Aug 2011 19:55:11 +0000 (UTC) Received: from muon.cran.org.uk (localhost [127.0.0.1]) by muon.cran.org.uk (Postfix) with ESMTP id 28079E6BFD; Mon, 29 Aug 2011 20:55:10 +0100 (BST) DKIM-Signature: v=1; a=rsa-sha1; c=relaxed; d=cran.org.uk; h=message-id :date:from:mime-version:to:cc:subject:references:in-reply-to :content-type:content-transfer-encoding; s=mail; bh=KwhPXnSxNz05 R+5M/lk7Bjj3GOA=; b=SIRl4p0FUqrmRjRSTPjj9NXR2aAlwU9XXRiPpnCknqPG fV2C/ZhzlfBO1n1IwGcjCVsIIC4WNegCVGwyTNpw1ZS/wGEqZQta06ZarhxNn6Fn rS2iQ4jhler5EKVd+ov5jyDCZf1P+Gcgh9Xd543f+dLu/pOHfE9bsUWZTKzF0dU= DomainKey-Signature: a=rsa-sha1; c=nofws; d=cran.org.uk; h=message-id :date:from:mime-version:to:cc:subject:references:in-reply-to :content-type:content-transfer-encoding; q=dns; s=mail; b=ZkXx9m kkZ53fuzNhyVg19soA2ZwhvHsdaFptoGvcGLYy6oCvKP4BsAvkuJCvDutUinvlj7 BF1L+iPTryG/O4+qnbY6fvh+xrnYrX+PuNvPJT7Ny4U98cTHiV6ke0VfoouldkR5 hxotSkYUovYpWp6xFN3Ypf4NOT1Xh9C7DOfc8= Received: from [192.168.1.104] (188-222-18-231.zone13.bethere.co.uk [188.222.18.231]) (using TLSv1 with cipher DHE-RSA-CAMELLIA256-SHA (256/256 bits)) (No client certificate requested) by muon.cran.org.uk (Postfix) with ESMTPSA id 07DD2E6B28; Mon, 29 Aug 2011 20:55:09 +0100 (BST) Message-ID: <4E5BEE9C.7080706@cran.org.uk> Date: Mon, 29 Aug 2011 20:55:08 +0100 From: Bruce Cran User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:6.0) Gecko/20110812 Thunderbird/6.0 MIME-Version: 1.0 To: Brett Glass References: <201108291724.LAA18734@lariat.net> In-Reply-To: <201108291724.LAA18734@lariat.net> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: questions@freebsd.org Subject: Re: Turn off hyperthreading on dual core Atom? X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 29 Aug 2011 19:55:12 -0000 On 29/08/2011 18:24, Brett Glass wrote: > With hyperthreading, the FreeBSD scheduler simply acts as if there are > 4 CPUs. Each "CPU" gets clock interrupts (which add overhead), and the > scheduler is naive about the fact that two of the "CPUs" are not > separate chips and could be held up if its mate has a heavy load. I do > not know if the supposed higher utilization of the resources on each > chip (including executing one thread while the CPU waits for data for > another) is worth it. What has your experience been? Actually, the ULE scheduler does know about HyperThreading and the topology of such CPUs. I don't know what it does with the information, but it probably works to optimize cache usage etc. -- Bruce Cran