Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761312Ab2BNWHz (ORCPT ); Tue, 14 Feb 2012 17:07:55 -0500 Received: from ogre.sisk.pl ([217.79.144.158]:52432 "EHLO ogre.sisk.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757335Ab2BNWHx (ORCPT ); Tue, 14 Feb 2012 17:07:53 -0500 From: "Rafael J. Wysocki" To: MyungJoo Ham Subject: Re: [RFC PATCH] PM / QoS: Introduce new classes: DMA-Throughput and DVFS-Latency Date: Tue, 14 Feb 2012 23:11:41 +0100 User-Agent: KMail/1.13.6 (Linux/3.3.0-rc3+; KDE/4.6.0; x86_64; ; ) Cc: linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, Len Brown , Pavel Machek , Kevin Hilman , Jean Pihet , markgross , kyungmin.park@samsung.com, myungjoo.ham@gmail.com References: <1329186372-2376-1-git-send-email-myungjoo.ham@samsung.com> In-Reply-To: <1329186372-2376-1-git-send-email-myungjoo.ham@samsung.com> MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-2" Content-Transfer-Encoding: 7bit Message-Id: <201202142311.41483.rjw@sisk.pl> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5993 Lines: 145 Hi, On Tuesday, February 14, 2012, MyungJoo Ham wrote: > 1. CPU_DMA_THROUGHPUT > > This might look simliar to CPU_DMA_LATENCY. However, there are H/W > blocks that creates QoS requirement based on DMA throughput, not > latency, while their (those QoS requester H/W blocks) services are > short-term bursts that cannot be effectively responsed by DVFS > mechanisms (CPUFreq and Devfreq). > > In the Exynos4412 systems that are being tested, such H/W blocks include > MFC (multi-function codec)'s decoding and enconding features, TV-out > (including HDMI), and Cameras. When the display is operated at 60Hz, > each chunk of task should be done within 16ms and the workload on DMA is > not well spread and fluctuates between frames; some frame requires more > and some do not and within a frame, the workload also fluctuates > heavily and the tasks within a frame are usually not parallelized; they > are processed through specific H/W blocks, not CPU cores. They often > have PPMU capabilities; however, they need to be polled very frequently > in order to let DVFS mechanisms react properly. (less than 5ms). > > For such specific tasks, allowing them to request QoS requirements seems > adequete because DVFS mechanisms (as long as the polling rate is 5ms or > longer) cannot follow up with them. Besides, the device drivers know > when to request and cancel QoS exactly. > > 2. DVFS_LATENCY > > Both CPUFreq and Devfreq have response latency to a sudden workload > increase. With near-100% (e.g., 95%) up-threshold, the average response > latency is approximately 1.5 x polling-rate. > > A specific polling rate (e.g., 100ms) may generally fit for its system; > however, there could be exceptions for that. For example, > - When a user input suddenly starts: typing, clicking, moving cursors, and > such, the user might need the full performance immediately. However, > we do not know whether the full performance is actually needed or not > until we calculate the utilization; thus, we need to calculate it > faster with user inputs or any similar events. Specifying QoS on CPU > processing power or Memory bandwidth at every user input is an > overkill because there are many cases where such speed-up isn't > necessary. > - When a device driver needs a faster performance response from DVFS > mechanism. This could be addressed by simply putting QoS requests. > However, such QoS requests may keep the system running fast > unnecessary in some cases, especially if a) the device's resource > usage bursts with some duration (e.g., 100ms-long bursts) and > b) the driver doesn't know when such burst come. MMC/WiFi often had > such behaviors although there are possibilities that part (b) might > be addressed with further efforts. > > The cases shown above can be tackled with putting QoS requests on the > response time or latency of DVFS mechanism, which is directly related to > its polling interval (if the DVFS mechanism is polling based). > > Signed-off-by: MyungJoo Ham > Signed-off-by: Kyungmin Park Who's going to use the new classes? Rafael > --- > include/linux/pm_qos.h | 6 +++++- > kernel/power/qos.c | 31 ++++++++++++++++++++++++++++++- > 2 files changed, 35 insertions(+), 2 deletions(-) > > diff --git a/include/linux/pm_qos.h b/include/linux/pm_qos.h > index e5bbcba..f8ccb7b 100644 > --- a/include/linux/pm_qos.h > +++ b/include/linux/pm_qos.h > @@ -13,13 +13,17 @@ > #define PM_QOS_CPU_DMA_LATENCY 1 > #define PM_QOS_NETWORK_LATENCY 2 > #define PM_QOS_NETWORK_THROUGHPUT 3 > +#define PM_QOS_CPU_DMA_THROUGHPUT 4 > +#define PM_QOS_DVFS_RESPONSE_LATENCY 5 > > -#define PM_QOS_NUM_CLASSES 4 > +#define PM_QOS_NUM_CLASSES 6 > #define PM_QOS_DEFAULT_VALUE -1 > > #define PM_QOS_CPU_DMA_LAT_DEFAULT_VALUE (2000 * USEC_PER_SEC) > #define PM_QOS_NETWORK_LAT_DEFAULT_VALUE (2000 * USEC_PER_SEC) > #define PM_QOS_NETWORK_THROUGHPUT_DEFAULT_VALUE 0 > +#define PM_QOS_CPU_DMA_THROUGHPUT_DEFAULT_VALUE 0 > +#define PM_QOS_DVFS_LAT_DEFAULT_VALUE (2000 * USEC_PER_SEC) > #define PM_QOS_DEV_LAT_DEFAULT_VALUE 0 > > struct pm_qos_request { > diff --git a/kernel/power/qos.c b/kernel/power/qos.c > index 995e3bd..b15e0b7 100644 > --- a/kernel/power/qos.c > +++ b/kernel/power/qos.c > @@ -101,11 +101,40 @@ static struct pm_qos_object network_throughput_pm_qos = { > }; > > > +static BLOCKING_NOTIFIER_HEAD(cpu_dma_throughput_notifier); > +static struct pm_qos_constraints cpu_dma_tput_constraints = { > + .list = PLIST_HEAD_INIT(cpu_dma_tput_constraints.list), > + .target_value = PM_QOS_CPU_DMA_THROUGHPUT_DEFAULT_VALUE, > + .default_value = PM_QOS_CPU_DMA_THROUGHPUT_DEFAULT_VALUE, > + .type = PM_QOS_MAX, > + .notifiers = &cpu_dma_throughput_notifier, > +}; > +static struct pm_qos_object cpu_dma_throughput_pm_qos = { > + .constraints = &cpu_dma_tput_constraints, > + .name = "cpu_dma_throughput", > +}; > + > + > +static BLOCKING_NOTIFIER_HEAD(dvfs_lat_notifier); > +static struct pm_qos_constraints dvfs_lat_constraints = { > + .list = PLIST_HEAD_INIT(dvfs_lat_constraints.list), > + .target_value = PM_QOS_DVFS_LAT_DEFAULT_VALUE, > + .default_value = PM_QOS_DVFS_LAT_DEFAULT_VALUE, > + .type = PM_QOS_MIN, > + .notifiers = &dvfs_lat_notifier, > +}; > +static struct pm_qos_object dvfs_lat_pm_qos = { > + .constraints = &dvfs_lat_constraints, > + .name = "dvfs_latency", > +}; > + > static struct pm_qos_object *pm_qos_array[] = { > &null_pm_qos, > &cpu_dma_pm_qos, > &network_lat_pm_qos, > - &network_throughput_pm_qos > + &network_throughput_pm_qos, > + &cpu_dma_throughput_pm_qos, > + &dvfs_lat_pm_qos, > }; > > static ssize_t pm_qos_power_write(struct file *filp, const char __user *buf, > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/