Messages in this thread | | | Date | Mon, 27 Feb 2012 15:14:30 +0900 | Subject | Re: [RFC PATCH] PM / QoS: Introduce new classes: DMA-Throughput and DVFS-Latency | From | MyungJoo Ham <> |
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On Sun, Feb 26, 2012 at 8:43 AM, Rafael J. Wysocki <rjw@sisk.pl> wrote: > 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
No. I've not posted the new version, yet, as I was waiting for other comments for this patch. I'll send a V2 patch with the omitted part included today.
Thanks.
Cheers! MyungJoo.
-- MyungJoo Ham, Ph.D. System S/W Lab, S/W Center, Samsung Electronics -- 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/
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