From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bart Van Assche Subject: Re: [PATCH] blk-ioprio: Introduce promote-to-rt policy Date: Wed, 8 Feb 2023 09:53:41 -0800 Message-ID: <7fcd4c38-ccbe-6411-e424-a57595ad9c0b@acm.org> References: <20230201045227.2203123-1-houtao@huaweicloud.com> <8c068af3-7199-11cf-5c69-a523c7c22d9a@acm.org> <4f7dcb3e-2d5a-cae3-0e1c-a82bcc3d2217@huaweicloud.com> <20230208134345.77bdep3kzp52haxu@quack3> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: Content-Language: en-US In-Reply-To: <20230208134345.77bdep3kzp52haxu@quack3> List-ID: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: Jan Kara Cc: Hou Tao , linux-block@vger.kernel.org, Jens Axboe , cgroups@vger.kernel.org, Tejun Heo , Zefan Li , Johannes Weiner , Jonathan Corbet , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, houtao1@huawei.com On 2/8/23 05:43, Jan Kara wrote: > On Fri 03-02-23 11:45:32, Bart Van Assche wrote: >> On 2/2/23 17:48, Hou Tao wrote: >>> I don't get it on how to remove IOPRIO_POL_PROMOTION when calculating the final >>> ioprio for bio. IOPRIO_POL_PROMOTION is not used for IOPRIO_CLASS values but >>> used to determinate on how to calculate the final ioprio for bio: choosing the >>> maximum or minimum between blkcg ioprio and original bio bi_ioprio. >> >> Do the block layer code changes shown below implement the functionality >> that you need? > > Just one question guys: So with my a78418e6a04c ("block: Always initialize > bio IO priority on submit") none-to-rt policy became effectively a noop as > Hou properly noticed. Are we aware of any users that were broken by this? > Shouldn't we rather fix the code so that none-to-rt starts to operate > correctly again? Or maybe change the none-to-rt meaning to be actually > promote-to-rt? > > I have to admit I'm wondering a bit what was the intended usecase behind > the introduction of none-to-rt policy. Can someone elaborate? promote-to-rt > makes some sense to me - we have a priviledged cgroup we want to provide > low latency access to IO but none-to-rt just does not make much sense to > me... Hi Jan, The test results I shared some time ago show that IOPRIO_CLASS_NONE was the default I/O priority two years ago (see also https://lore.kernel.org/linux-block/20210927220328.1410161-5-bvanassche@acm.org/). The none-to-rt policy increases the priority of bio's that have not been assigned an I/O priority to RT. Does this answer your question? Thanks, Bart.