From owner-svn-src-head@freebsd.org Fri Mar 2 14:14:13 2018 Return-Path: Delivered-To: svn-src-head@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id D45B9F26FD9; Fri, 2 Mar 2018 14:14:13 +0000 (UTC) (envelope-from pieter@degoeje.nl) Received: from mo6-p00-ob.smtp.rzone.de (mo6-p00-ob.smtp.rzone.de [IPv6:2a01:238:20a:202:5300::3]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client CN "*.smtp.rzone.de", Issuer "TeleSec ServerPass DE-2" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 25ABE82CD1; Fri, 2 Mar 2018 14:14:13 +0000 (UTC) (envelope-from pieter@degoeje.nl) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; t=1520000052; s=strato-dkim-0002; d=degoeje.nl; h=Content-Transfer-Encoding:Content-Type:In-Reply-To:Date:Message-ID: From:References:To:Subject:X-RZG-CLASS-ID:X-RZG-AUTH; bh=EC4U1TGW7mQdV/MlNVmdh0fqqPUN33TCc3JmWi2MtKs=; b=PwvVS2ZIWLyHGw6tCzc8eE+0cbSnt3rxZiwwwsy1AcnJrYK19j5lpKjupTBfht8zS9 mTZGKj/y9XN6VCjECgqxQPkv3mkssGCi17U6VE2DPnjJ6jAkumuxffw22jYkhcP570tu Ol4C296ZDfM+oZzGgMQe0msKdHoWH0OFQZ5+nFhDgzMOetUK8hxGQ4sS3OPAKeoN7dl6 Ys0AFFyCKVlO1H6JO/YiW6wRP/vuSWwzNJvBXEz3FLEMKinN279fUiaiURpLqoC/gxxR XyC6YI+a/uL8aD4OYYFOeiMd11rpGib4nBudqkXRu4oP5Z1NNmA/MZpzNn7DNxPFSPsv I9UA== X-RZG-AUTH: :PGUBYUW6W/vjKUwSpXdHbXp/KlnzhfjpGaq9ccFSB01ZbYSz0XXyHEnBMb8k5m4K X-RZG-CLASS-ID: mo00 Received: from [192.168.1.81] ([31.200.213.82]) by smtp.strato.com (RZmta 42.18 AUTH) with ESMTPSA id N065ceu22EE8Yoj (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (curve secp521r1 with 521 ECDH bits, eq. 15360 bits RSA)) (Client did not present a certificate); Fri, 2 Mar 2018 15:14:08 +0100 (CET) Subject: Re: svn commit: r329882 - in head/sys: conf kern sys vm To: Jeff Roberson , src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org References: <201802232251.w1NMpqn4025101@repo.freebsd.org> From: Pieter de Goeje Message-ID: <1782e475-06d8-c806-0d0c-ae5a5893baf5@degoeje.nl> Date: Fri, 2 Mar 2018 15:14:08 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 MIME-Version: 1.0 In-Reply-To: <201802232251.w1NMpqn4025101@repo.freebsd.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.25 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 02 Mar 2018 14:14:14 -0000 Hi, I'm curious, it looks like Kd is quite significant by default, I assume to limit the slew rate of the output. Given that the error is an integer, and pidctrl_daemon() is called at irregular intervals, it seems to me that the derivative will be very noisy. In my experience with PID controllers controlling physical processes, one would need some kind of filtering on the input to make Kd useful, otherwise it would just contribute more instability to the system. In practice even a simple exponential (single pole) filter can help a lot at the cost of increased response time. Is this something that was considered? - Pieter de Goeje