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[91.78.208.152]) by smtp.googlemail.com with ESMTPSA id v9sm13821994ljv.82.2020.04.08.07.21.39 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 08 Apr 2020 07:21:40 -0700 (PDT) Subject: Re: [RFC PATCH v6 6/9] media: tegra: Add Tegra210 Video input driver To: Sowjanya Komatineni , thierry.reding@gmail.com, jonathanh@nvidia.com, frankc@nvidia.com, hverkuil@xs4all.nl, sakari.ailus@iki.fi, helen.koike@collabora.com Cc: sboyd@kernel.org, linux-media@vger.kernel.org, devicetree@vger.kernel.org, linux-clk@vger.kernel.org, linux-tegra@vger.kernel.org, linux-kernel@vger.kernel.org References: <1585963507-12610-1-git-send-email-skomatineni@nvidia.com> <08cd31d5-e8b9-4d3a-fb0e-0e4462947d96@nvidia.com> <12a834ac-52b1-6dc0-7d3a-3e6a1fa85a2a@gmail.com> <760d071e-0cbc-b3eb-9231-fb9f9ecb44a6@nvidia.com> <9e317f65-8a02-3b15-cfec-8e0d8374130e@gmail.com> <97b35910-4c93-123a-43a0-eb14476ed0f3@nvidia.com> <84ad4e2d-6ac1-e1f4-1c55-5edaae850631@nvidia.com> <15a879b3-8fb9-6821-3cdc-104ba583ac12@gmail.com> <0c425505-347f-7418-af7e-d121fe0d06dc@nvidia.com> <1a31cd60-739f-0660-1c45-31487d2f2128@nvidia.com> <603084a5-249a-4fe2-3646-e9335ef9ab43@nvidia.com> <7895b9c6-f27d-8939-73d7-67d785e1a8b7@nvidia.com> From: Dmitry Osipenko Message-ID: Date: Wed, 8 Apr 2020 17:21:39 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 08.04.2020 03:00, Sowjanya Komatineni пишет: ... >>>>> I suppose that taking a shot takes at least few milliseconds, which >>>>> should be unacceptable to waste. >>>> As long as buffers are in queue we have to keep processing each >>>> buffer and between buffers obviously we have to wait for previous >>>> frames to finish and this why we have separate thread for frame >>>> finish where we can have next buffer capture ready and issue while >>>> previous frame memory write happens >> Also we specified numbers buffers as 3 to vb2 queue. So this is rare >> case but to prevent issuing more than 2 at a time as VI HW is only >> double buffered and syncpt fifo max depth is 2 added this to be safer. > > To be more clear, when more buffers are enqueued from userspace always > capture list will be full and thread will be busy in capture till either > error or stop stream request happens. > If kthreads take more than 1% of CPU time during capture (video) with more than 2 buffers in queue, then it's not good and I think you should do something about it. If kthreads stay at ~0%, then it should be okay as-is.