From owner-freebsd-net@FreeBSD.ORG Tue Apr 10 23:14:27 2012 Return-Path: Delivered-To: net@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id DC89B106566C; Tue, 10 Apr 2012 23:14:27 +0000 (UTC) (envelope-from barney@pit.databus.com) Received: from out.smtp-auth.no-ip.com (smtp-auth.no-ip.com [8.23.224.61]) by mx1.freebsd.org (Postfix) with ESMTP id B0DB18FC1A; Tue, 10 Apr 2012 23:14:27 +0000 (UTC) X-No-IP: databus.com@noip-smtp X-No-IP: databus.com@noip-smtp X-No-IP: databus.com@noip-smtp X-No-IP: databus.com@noip-smtp X-Report-Spam-To: abuse@no-ip.com Received: from smtp-auth.no-ip.com (unknown [172.20.20.61]) (Authenticated sender: databus.com@noip-smtp) by smtp-auth.no-ip.com (Postfix) with ESMTPA id D8BC1400AE5; Tue, 10 Apr 2012 16:05:03 -0700 (PDT) Received: from pit.databus.com (localhost [127.0.0.1]) by pit.databus.com (8.14.5/8.14.5) with ESMTP id q3AN50cV032034 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Tue, 10 Apr 2012 19:05:01 -0400 (EDT) (envelope-from barney@pit.databus.com) X-DKIM: OpenDKIM Filter v2.4.3 pit.databus.com q3AN50cV032034 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=databus.com; s=20091218; t=1334099101; bh=EPhSfPa8ORbA+mlrPRKHrzJxWo4cwxc1v8Bnulkjs+k=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:In-Reply-To; b=m6O+edhSB2YaEA4sHQAUzjMBcuadBmVtc9gZM6Uo5kxhZ5h/U0UJGFONeEvmuvIhn nhAu/7UNKN5JgZOx2owgnis/WgBPT2REHRu/jGqSmBPhjTxhWthHn3WcSQVmNUkv20 hF5i0WzE3jaG3hmljBTn8MwZglyXtl05D6IilCcc= Received: (from barney@localhost) by pit.databus.com (8.14.5/8.14.5/Submit) id q3AN5028032033; Tue, 10 Apr 2012 19:05:00 -0400 (EDT) (envelope-from barney) Date: Tue, 10 Apr 2012 19:05:00 -0400 From: Barney Wolff To: Julian Elischer Message-ID: <20120410230500.GA22829@pit.databus.com> References: <20120410225257.GB53350@onelab2.iet.unipi.it> <4F84B6DB.5040904@freebsd.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4F84B6DB.5040904@freebsd.org> User-Agent: Mutt/1.5.21 (2010-09-15) Cc: Luigi Rizzo , current@freebsd.org, net@freebsd.org Subject: Re: strange ping response times... X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 10 Apr 2012 23:14:28 -0000 CPU cache? Cx states? powerd? On Tue, Apr 10, 2012 at 03:40:27PM -0700, Julian Elischer wrote: > On 4/10/12 3:52 PM, Luigi Rizzo wrote: > > I noticed this first on a 10G interface, but now there seems > > to be a similar issue on the loopback. > > > > Apparently a ping -f has a much lower RTT than one with non-zero > > delay between transmissions. Part of the story could be that > > the flood version invokes a non-blocking select. > > On the other hand, pinging on the loopback should make > > the response available right away, so what could be the reason > > for the additional 3..10us in the ping response time ? > > > > The following are numbers on an i7-2600k at 3400 MHz + turboboost, > > running stable/9 amd64. Note how the min ping time significantly > > increases moving from flood to 10ms to 1s. > > On an Intel 10G interface i am seeing a min of 14-16us with > > a ping flood, and up to 33-35us with the standard 1s interval > > (using -q probably trims another 2..5us) > > I'd suggest some ktr points around the loopback path..