Messages in this thread | | | From | "Rafael J. Wysocki" <> | Subject | Re: [RFC PATCH] PM / QoS: Introduce new classes: DMA-Throughput and DVFS-Latency | Date | Sun, 26 Feb 2012 00:43:50 +0100 |
| |
On Tuesday, February 14, 2012, MyungJoo Ham wrote: > On Tue, Feb 14, 2012 at 11:26 AM, MyungJoo Ham <myungjoo.ham@samsung.com> 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 <myungjoo.ham@samsung.com> > > Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com> > > In this PM-QoS patch, register_pm_qos_misc() for the new classes in > pm_qos_power_init() is missing. > > Those will be included in the next version of the patch.
Has the new version been posted already? I seem to have missed it if so.
Thanks, Rafael
| |