Hi Chanwoo, On 7/3/20 8:26 AM, Chanwoo Choi wrote: > Add the delayed timer to devfreq framework in order to support > the periodical polling mode without stop caused by CPU idle state. Thank you, this patchset looks fine to me and is a step in the right direction: Reviewed-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@xxxxxxxxxxx> > Some Non-CPU device must need to monitor the device status like > utilization regardless of CPU state. This is probably true for all devfreq devices using simple_ondemand governor by default: drivers/devfreq/exynos-bus.c drivers/devfreq/rk3399_dmc.c drivers/devfreq/tegra20-devfreq.c drivers/gpu/drm/lima/lima_devfreq.c drivers/gpu/drm/msm/msm_gpu.c drivers/gpu/drm/panfrost/panfrost_devfreq.c drivers/memory/samsung/exynos5422-dmc.c drivers/scsi/ufs/ufshcd.c With devfreq device polling being "coupled" to CPU idle state the devfreq subsystem behavior is completely unpredictable and unreliable. It affects both performance (device opp change up happening too late) and power consumption (device opp change down happening too late). It also causes hardware usage counters support to report too high values (because of CPU idle "coupling" the real polling period becomes larger than maximum period supported by the counter and the counter becomes fully "saturated") which negatively affects power consumption (as has been observed when using Odroid XU3/4). [ The only upside of using such "coupling" is lowered CPU power usage (in some situations) but at the (unacceptable IMHO) cost of the correctness of operations of devfreq subsystem. ] Unfortunately this patchset currently fixes only exynos5422-dmc devfreq driver. To fix problems for Exynos platforms we need to also fix exynos-bus devfreq driver. Best regards, -- Bartlomiej Zolnierkiewicz Samsung R&D Institute Poland Samsung Electronics > - patch1 explains the detailed reason why the delayed timer is required. > - patch2 initializes that exynos5422-dmc device use delayed timer as default > instead of deferrable timer. > > Chanwoo Choi (2): > PM / devfreq: Add support delayed timer for polling mode > memory: samsung: exynos5422-dmc: Use delayed timer as default > > Documentation/ABI/testing/sysfs-class-devfreq | 12 +++ > drivers/devfreq/devfreq.c | 83 ++++++++++++++++++- > drivers/memory/samsung/exynos5422-dmc.c | 1 + > include/linux/devfreq.h | 9 ++ > 4 files changed, 104 insertions(+), 1 deletion(-)
