From owner-freebsd-questions@FreeBSD.ORG Mon Dec 15 05:40:45 2014 Return-Path: Delivered-To: freebsd-questions@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 A4966226; Mon, 15 Dec 2014 05:40:45 +0000 (UTC) Received: from mail-wi0-x22a.google.com (mail-wi0-x22a.google.com [IPv6:2a00:1450:400c:c05::22a]) (using TLSv1 with cipher ECDHE-RSA-RC4-SHA (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 356846BE; Mon, 15 Dec 2014 05:40:45 +0000 (UTC) Received: by mail-wi0-f170.google.com with SMTP id bs8so9382357wib.5; Sun, 14 Dec 2014 21:40:43 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type; bh=TYfeKmNSf2onnVhAIJddaJMwmYBpZElFVcKdPC0lNxQ=; b=XFUJbfkBZRua5jk9yQd59evGDscZskmWsdKAv9DZj1X9HH5K+gNzhkk5+xzfM1gg8D Sjx6qbHaO6E+z09XGtOQI09o6z21bFOXP/aEMZwglUicpjGSpC0Xzzbf10NQQSgC48Uv hVKrwkYnCtsjRWO5+f1pG1eJYdCG6nuWip2DOQYaxhmVTqZZ3yESeNQmx1kMlOrX4UEv n5tGEo82TNM93CN6NNPsV4HLsloq/IaTZ922Ku4pIB3frLOYHUpHnmzSZtr9/xnAqHkL saDycMWmmMwRtjdvGZPf50iv2WyHSK2AQnNbyRogrlrhnxUajcDj+UEqVxLnYxuL9/G/ lvUw== MIME-Version: 1.0 X-Received: by 10.180.198.164 with SMTP id jd4mr27839128wic.42.1418622043689; Sun, 14 Dec 2014 21:40:43 -0800 (PST) Received: by 10.216.106.134 with HTTP; Sun, 14 Dec 2014 21:40:43 -0800 (PST) In-Reply-To: References: <20141208153925.5df90587@prometheus> Date: Mon, 15 Dec 2014 00:40:43 -0500 Message-ID: Subject: Re: HyperThreading on Intel Xeon Haswell, a benefit? From: grarpamp To: FreeBSD Questions Content-Type: text/plain; charset=UTF-8 Cc: FreeBSD Mailing Lists , "freebsd-hardware@freebsd.org" X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 15 Dec 2014 05:40:45 -0000 On Wed, Dec 10, 2014 at 8:19 AM, Jia-Shiun Li wrote: > Yes, Haswell has an additional store addr but still only one store data unit. > > http://www.tomshardware.com/reviews/core-i7-4770k-haswell-review,3521.html > > But I guess they'd argue that they meant to saturate memory > channels with all available cores as possible first, and additional > threads are only for last resort. And that's probably what the most > schedulers do. > > I benchmarked it on a 4th gen i3. Buildkernel got 5~10% benefit IIRC. > The best way to tell is still to conduct tests with your own workload. > If the claimed 5% transistor cost brings 10% benefits, that's already > a win. OTTH how much you paid for it is another story. Where is the claim of "5% transistor cost" from? I don't see it linked in this thread. Is it in terms of $ as a sales feature to get HT/SMT, or transistor count to get it? I think SMT transistor count could change over CPU generations optimized. Any bump in price to get HT, is amortized over time. Any bump in performance due to HT, is integrated over time. A watt costs about $1/yr. If SMT is 5% faster, over 4hr saves 12 minutes of your time, which saves $n/day, which more than pays for purchase and watts. If it is slower, it hurts similarly $hard unless you turn it off and eat its purchase difference. Thus to see what people were seeing perf wise.