From owner-freebsd-stable@freebsd.org Mon Aug 14 07:16:34 2017 Return-Path: Delivered-To: freebsd-stable@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id C5C79DD9BC6 for ; Mon, 14 Aug 2017 07:16:34 +0000 (UTC) (envelope-from prvs=03993fbaa3=ari@ish.com.au) Received: from fish.ish.com.au (ip-2.ish.com.au [203.29.62.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 8EC9071344 for ; Mon, 14 Aug 2017 07:16:33 +0000 (UTC) (envelope-from prvs=03993fbaa3=ari@ish.com.au) Received: from ip-136.ish.com.au ([203.29.62.136]:64855) by fish.ish.com.au with esmtpsa (TLSv1.2:AES128-SHA:128) (Exim 4.82_1-5b7a7c0-XX) (envelope-from ) id 1dh9bq-0001MZ-0f; Mon, 14 Aug 2017 17:16:22 +1000 X-CTCH-RefID: str=0001.0A150205.59914E46.0061:SCFSTAT42589845, ss=1, re=-4.000, recu=0.000, reip=0.000, cl=1, cld=1, fgs=0 Subject: Re: TSC timekeeping and cpu states To: Kevin Oberman Cc: freebsd-stable References: From: Aristedes Maniatis Message-ID: <2ef99f5e-46f5-a185-2ac3-67d6afe68c89@ish.com.au> Date: Mon, 14 Aug 2017 17:16:22 +1000 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:56.0) Gecko/20100101 Thunderbird/56.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-AU Content-Transfer-Encoding: 7bit X-BeenThere: freebsd-stable@freebsd.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Production branch of FreeBSD source code List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 14 Aug 2017 07:16:34 -0000 On 14/8/17 3:08PM, Kevin Oberman wrote: > Again, the documentation lags reality. The default was changed for 11.0. It is still conservative. In ALMOST all cases, Cmax will yield the bast results. However, on large systems with many cores, Cmax will trigger very poor results, so the default is C2, just to be safe. > > As far as possible TSC impact, I think older processors had TSC issues when not all cores ran with the same clock speed. That said, I am not remotely expert on such issues, so don't take this too seriously. Thanks Kevin What does 'large' and 'many cores' mean here? Is 24 cores large or small? For a server do we ever want the CPU to enter states other than C1? Ari -- --------------------------> Aristedes Maniatis CEO, ish https://www.ish.com.au GPG fingerprint CBFB 84B4 738D 4E87 5E5C 5EFA EF6A 7D2E 3E49 102A