From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751261AbWGDK06 (ORCPT ); Tue, 4 Jul 2006 06:26:58 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751264AbWGDK06 (ORCPT ); Tue, 4 Jul 2006 06:26:58 -0400 Received: from nf-out-0910.google.com ([64.233.182.190]:64093 "EHLO nf-out-0910.google.com") by vger.kernel.org with ESMTP id S1751261AbWGDK05 (ORCPT ); Tue, 4 Jul 2006 06:26:57 -0400 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=beta; d=gmail.com; h=received:message-id:date:from:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references; b=nLzo1TfHY4ZzBb5cQRfWuae6I3D8ilo8WeqrHB8V5WE9AKJCnG4Tb4mxnPb1BKpI4+N72Er0jJEhiT7uQXIxoSQxo9kNMgIhtCHyo9aShZHAuUI0rBKtorOnaQlGDnD1dHa14YnH0/ZfZ9yMgHeKE1nhxNEVMwCKQce/6STZQUg= Message-ID: <41840b750607040326y7bfe92dy21c6845ab034ce30@mail.gmail.com> Date: Tue, 4 Jul 2006 13:26:56 +0300 From: "Shem Multinymous" To: "Pavel Machek" Subject: Re: [Hdaps-devel] Generic interface for accelerometers (AMS, HDAPS, ...) Cc: "Henrique de Moraes Holschuh" , "Stelian Pop" , "Michael Hanselmann" , hdaps-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org, lm-sensors@lm-sensors.org In-Reply-To: <20060704075950.GA13073@elf.ucw.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <20060703124823.GA18821@khazad-dum.debian.net> <20060704075950.GA13073@elf.ucw.cz> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On 7/4/06, Pavel Machek wrote: > Just use input infrastructure and be done with that? You can do > parking from userspace. Will moving the hdapsd userspace daemon from sysfs polling to the input infrastructure cause a noticable latency increase compared to polling sysfs? This functionality is highly time-critical. Also, there's a small issue with polling frequency. hdapsd needs a fairly high frequency (say, 50Hz) to gather statistics and keep response latency low, whereas the hdaps driver's internal polling (routing to the input infrastructure) is currently done at only 20Hz. We'll need to increase the latter, thereby slightly increasing system load when hdaps isn't running. In terms of magnitude, an hdaps readout takes ~70usec on average and (very rarely) up to ~1msec. This is with the tp_smapi [1] patches to hdaps, which add the checks and retries needed to ensure the readout is valid. BTW, can the driver tell when nothing is accessing its input device, and avoid polling in that case? Shem [1] http://thinkwiki.org/wiki/tp_smapi