From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kevin Hilman Subject: Re: [PATCH 3/3] OMAP: omap_device: optionally auto-adjust device activate/deactivate latencies Date: Mon, 23 Nov 2009 10:35:47 -0800 Message-ID: <4B0AD603.3050609@deeprootsystems.com> References: <1258997622-13923-1-git-send-email-khilman@deeprootsystems.com> <1258997622-13923-2-git-send-email-khilman@deeprootsystems.com> <1258997622-13923-3-git-send-email-khilman@deeprootsystems.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from mail-pz0-f171.google.com ([209.85.222.171]:47125 "EHLO mail-pz0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754188AbZKWSfn (ORCPT ); Mon, 23 Nov 2009 13:35:43 -0500 Received: by pzk1 with SMTP id 1so4142979pzk.33 for ; Mon, 23 Nov 2009 10:35:49 -0800 (PST) In-Reply-To: <1258997622-13923-3-git-send-email-khilman@deeprootsystems.com> Sender: linux-omap-owner@vger.kernel.org List-Id: linux-omap@vger.kernel.org To: linux-omap@vger.kernel.org Kevin Hilman wrote: > First, this patch adds new worst-case latency values to the > omap_device_pm_latency struct. Here the worst-case measured latencies > for the activate and deactivate hooks are stored. > > In addition, add an option to auto-adjust the latency values used for > device activate/deactivate. > > By setting a new 'OMAP_DEVICE_LATENCY_AUTO_ADJUST' flag in the > omap_device_pm_latency struct, the omap_device layer automatically > adjusts the activate/deactivate latencies to the worst-case measured > values. > > Anytime a new worst-case value is found, it is printed to the console. > Here is an example log during boot using UART2 s an example. After > boot, the OPP is manually changed to the 125MHz OPP: > > [...] > Freeing init memory: 128K > omap_device: serial8250.2: new worst case deactivate latency 0: 30517 > omap_device: serial8250.2: new worst case activate latency 0: 30517 > omap_device: serial8250.2: new worst case activate latency 0: 218139648 > omap_device: serial8250.2: new worst case deactivate latency 0: 61035 > omap_device: serial8250.2: new worst case activate latency 0: 278076171 > omap_device: serial8250.2: new worst case activate latency 0: 298614501 > omap_device: serial8250.2: new worst case activate latency 0: 327331542 > > / # echo 125000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed > > omap_device: serial8250.2: new worst case deactivate latency 0: 91552 > > Motivation: this can be used as a technique to automatically determine > the worst case latency values. The current method of printing a > warning on every violation is too noisy to actually interact the > console in order to set low OPP to discover latencies. Another motivation for this patch is that the activate/deactivate latenices can vary depending on the idlemode of the device. While working on the UART I noticed that when using no-idle, the activate latencies were as high as several hundred msecs as shown above. When the UARTs are in smart-idle, the max latency is well under 100 usecs. Kevin