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Wed, 8 Jul 2020 10:52:54 +0000 (GMT) Subject: Re: [RFC PATCH 0/2] PM / devfreq: Add delayed timer for polling To: Chanwoo Choi Cc: lukasz.luba@arm.com, k.konieczny@samsung.com, krzk@kernel.org, kgene@kernel.org, s.nawrocki@samsung.com, willy.mh.wolff.ml@gmail.com, chanwoo@kernel.org, myungjoo.ham@samsung.com, kyungmin.park@samsung.com, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-samsung-soc@vger.kernel.org, linux-arm-kernel@lists.infradead.org From: Bartlomiej Zolnierkiewicz Message-ID: Date: Wed, 8 Jul 2020 12:52:53 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20200703062622.11773-1-cw00.choi@samsung.com> Content-Language: en-US Content-Transfer-Encoding: 7bit X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFrrMKsWRmVeSWpSXmKPExsWy7djP87rtS1njDY7NUrWYeOMKi8X1L89Z LRZ8msFq0f/4NbPF+fMb2C3ONr1ht9j0+BqrxeVdc9gsPvceYbSYcX4fk8XCphZ2i9uNK9gs Dr9pZ7X4duIRowOfx5p5axg9ds66y+6xaVUnm8fmJfUefVtWMXp83iQXwBbFZZOSmpNZllqk b5fAlfH3yU7Wgm/CFWsW/GFuYJwt0MXIySEhYCJxbeVSxi5GLg4hgRWMEntmr2KBcL4wSsx/ d58JwvnMKHFg+Sd2mJaTbz5DtSxnlFja8wzKecsoMf3HCmaQKmEBD4m797vBOkQENCRm/r0C VsQscItJ4tThG4wgCTYBK4mJ7avAbF4BO4mFV26CNbMIqEj8P3CVCcQWFYiQ+PTgMCtEjaDE yZlPWEBsTgFriTs999hAbGYBcYlbT+YzQdjyEtvfzmEGWSYh8JZd4veNu8wQd7tIfDnwCuoH YYlXx7dA2TISpyf3sEA0rGOU+NvxAqp7O6PE8sn/2CCqgNad+wVkcwCt0JRYv0sfxJQQcJS4 1CUFYfJJ3HgrCHEDn8SkbdOZIcK8Eh1tQhAz1CQ2LNvABrO1a+dK5gmMSrOQfDYLyTezkHwz C2HtAkaWVYziqaXFuempxYZ5qeV6xYm5xaV56XrJ+bmbGIFJ7fS/4592MH69lHSIUYCDUYmH NyORJV6INbGsuDL3EKMEB7OSCK/T2dNxQrwpiZVVqUX58UWlOanFhxilOViUxHmNF72MFRJI TyxJzU5NLUgtgskycXBKNTC6TEhKsdwrlboobJ1PvaLfus16S86funKyW4f5g3DwhLX/7P9M 2XMy9Ntua+73r/sUjLTuHLjioWC4ccbFJQwfWNdeOJ29Iyhhe0RV1OygBgfe73NWnfa5sXTB Htf0Sa4Cp9/71V+zSzO7fO51rkZmQswWTU0uwXsXZh86tvD5v7PGl0Jfhn/eqsRSnJFoqMVc VJwIAAvvUe1mAwAA X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFnrEIsWRmVeSWpSXmKPExsVy+t/xe7rtS1njDVZ/F7SYeOMKi8X1L89Z LRZ8msFq0f/4NbPF+fMb2C3ONr1ht9j0+BqrxeVdc9gsPvceYbSYcX4fk8XCphZ2i9uNK9gs Dr9pZ7X4duIRowOfx5p5axg9ds66y+6xaVUnm8fmJfUefVtWMXp83iQXwBalZ1OUX1qSqpCR X1xiqxRtaGGkZ2hpoWdkYqlnaGwea2VkqqRvZ5OSmpNZllqkb5egl/H3yU7Wgm/CFWsW/GFu YJwt0MXIySEhYCJx8s1nxi5GLg4hgaWMEg+XfgJyOIASMhLH15dB1AhL/LnWxQZR85pR4lFH CxtIQljAQ+Lu/W52EFtEQENi5t8rjCA2s8AtJokVr0JB5ggJ9DFKfIoDCbMJWElMbF8FVsIr YCex8MpNZhCbRUBF4v+Bq0wgtqhAhMThHbOgagQlTs58wgJicwpYS9zpuccGMV5d4s+8S8wQ trjErSfzmSBseYntb+cwT2AUmoWkfRaSlllIWmYhaVnAyLKKUSS1tDg3PbfYSK84Mbe4NC9d Lzk/dxMjMH63Hfu5ZQdj17vgQ4wCHIxKPLwZiSzxQqyJZcWVuYcYJTiYlUR4nc6ejhPiTUms rEotyo8vKs1JLT7EaAr03ERmKdHkfGBqySuJNzQ1NLewNDQ3Njc2s1AS5+0QOBgjJJCeWJKa nZpakFoE08fEwSnVwJhqd0DUlXGCz9YDIYH1E6eYyzzMPq23TvBdxddJt7OPC0+5bXGhilXM K8hHJeuVRMgsH1/9NPEv5VVp/IaOuyYb/nnx/a2w9AuPn29Xdfv4f7/yksHgJLNAjYdarTz7 78P6rS+k/lwQbl2xs0nh2CyFFVHv07aIHZQ7PVEi/FSrILdo+S3PiUosxRmJhlrMRcWJACZW R3/1AgAA X-CMS-MailID: 20200708105255eucas1p229180d35b47e4a350fbb72ea5e2df2a9 X-Msg-Generator: CA Content-Type: text/plain; charset="utf-8" X-RootMTR: 20200703061508epcas1p171aa3c0ab832b77e5837d8bd1e563742 X-EPHeader: CA CMS-TYPE: 201P X-CMS-RootMailID: 20200703061508epcas1p171aa3c0ab832b77e5837d8bd1e563742 References: <20200703062622.11773-1-cw00.choi@samsung.com> Sender: linux-samsung-soc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-samsung-soc@vger.kernel.org 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 > 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(-)