From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7F1CAC433E0 for ; Mon, 22 Feb 2021 13:46:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4B83064DDC for ; Mon, 22 Feb 2021 13:46:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231598AbhBVNpe (ORCPT ); Mon, 22 Feb 2021 08:45:34 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48992 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232053AbhBVNnm (ORCPT ); Mon, 22 Feb 2021 08:43:42 -0500 Received: from mail-wm1-x333.google.com (mail-wm1-x333.google.com [IPv6:2a00:1450:4864:20::333]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 20933C061797; Mon, 22 Feb 2021 05:42:44 -0800 (PST) Received: by mail-wm1-x333.google.com with SMTP id l13so4846171wmg.5; Mon, 22 Feb 2021 05:42:44 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=EokPmjsgtfLr/Ht3Tl2sy1hHZqSDcon8nbXZDyMDp44=; b=J5tKeePzyvCR1SlPSDb1w6I+IgKDdVtV0hiWmwZPNYDwwLhBwTrasjQW3m40fTQ1Lt d0AK3lNiNFi3at56v727sk2bhUwWNgp2vsWAdeqUSgHDqlfNKkj+g4hyhITWPT7VSezu bOQBKvIY9E+XnTKcWq4mJ3MwAhv5HGD5Yf2B47WUdsvem5cmyOKmurX6bpNLwF1PmUb5 Jsxu9cU5d3blgFXdCiJZrl3RkJmn1ZUe7eanxYI3fZw0DJB7zPFkVjh+gNAeYQL1Mm4r wvIzNPXueFqJl42T61yvFMipBHgVsS9hZFqOgi/BG0U/1jdiLAgFBV4fxptyvZCf58VZ WFPA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=EokPmjsgtfLr/Ht3Tl2sy1hHZqSDcon8nbXZDyMDp44=; b=dmLDBFLWgWm5oXqtHimtSTBvmmkY5PyX0VPFVNLIy2OIIeSph2C+GoBC8xHlFjleYu j3f9GFuM7yieu9S3u9XWKjtenyhqy8rkSzZm0VSF+RNwn/Oj2CFIrRy7xn9nBXe1FsRS jfSxzvZv94nvPCcWI9KOsD1dC7g3W0Dn7chYsDgE1uZhhfXyxe8TH91Pwkczp7oiqmzE n5K4h0ZC7ypAyy+QUgn0kV7LJ5lbmuNj2LdeoKSopBuf0Hv8+GxhugBoAL8YzCtxY/nM aD5vYiClKW0nCqzLc6NGl6s2SX7M/sF8L535SgGByKehH/ge9k6+RnZgWQ/WOyq/ayaY CDVw== X-Gm-Message-State: AOAM532PYhSjGY4aWZ4pzPW6hT9+K8rPJmwBqW5bI9/0GB+ZOfz7Rh2U CGpdOr22wdDhZ6pSOg/uNt7BUVItiO3y0sYJZ+Q= X-Google-Smtp-Source: ABdhPJyKoim3/GDB0UpkwqwBKU/AY5ujt7EE/+q9PZBcBIJnUofaxL5JR2azM46w7FqtA5BNFld6Q5Wi0+SjT66z0Rg= X-Received: by 2002:a1c:2cc4:: with SMTP id s187mr15312085wms.4.1614001362757; Mon, 22 Feb 2021 05:42:42 -0800 (PST) MIME-Version: 1.0 References: <20210127150029.13766-1-joshi.k@samsung.com> <489691ce-3b1e-30ce-9f72-d32389e33901@gmail.com> <2d37d0ca-5853-4bb6-1582-551b9044040c@kernel.dk> In-Reply-To: From: Kanchan Joshi Date: Mon, 22 Feb 2021 19:12:18 +0530 Message-ID: Subject: Re: [RFC PATCH 0/4] Asynchronous passthrough ioctl To: Jens Axboe Cc: Pavel Begunkov , Kanchan Joshi , Keith Busch , Christoph Hellwig , sagi@grimberg.me, linux-nvme@lists.infradead.org, io-uring@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Javier Gonzalez , Nitesh Shetty , Selvakumar S Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On Thu, Jan 28, 2021 at 10:54 PM Jens Axboe wrote: > > On 1/28/21 10:13 AM, Kanchan Joshi wrote: > > On Thu, Jan 28, 2021 at 8:08 PM Jens Axboe wrote: > >> > >> On 1/28/21 5:04 AM, Kanchan Joshi wrote: > >>> On Wed, Jan 27, 2021 at 9:32 PM Pavel Begunkov wrote: > >>>> > >>>> On 27/01/2021 15:42, Pavel Begunkov wrote: > >>>>> On 27/01/2021 15:00, Kanchan Joshi wrote: > >>>>>> This RFC patchset adds asynchronous ioctl capability for NVMe devices. > >>>>>> Purpose of RFC is to get the feedback and optimize the path. > >>>>>> > >>>>>> At the uppermost io-uring layer, a new opcode IORING_OP_IOCTL_PT is > >>>>>> presented to user-space applications. Like regular-ioctl, it takes > >>>>>> ioctl opcode and an optional argument (ioctl-specific input/output > >>>>>> parameter). Unlike regular-ioctl, it is made to skip the block-layer > >>>>>> and reach directly to the underlying driver (nvme in the case of this > >>>>>> patchset). This path between io-uring and nvme is via a newly > >>>>>> introduced block-device operation "async_ioctl". This operation > >>>>>> expects io-uring to supply a callback function which can be used to > >>>>>> report completion at later stage. > >>>>>> > >>>>>> For a regular ioctl, NVMe driver submits the command to the device and > >>>>>> the submitter (task) is made to wait until completion arrives. For > >>>>>> async-ioctl, completion is decoupled from submission. Submitter goes > >>>>>> back to its business without waiting for nvme-completion. When > >>>>>> nvme-completion arrives, it informs io-uring via the registered > >>>>>> completion-handler. But some ioctls may require updating certain > >>>>>> ioctl-specific fields which can be accessed only in context of the > >>>>>> submitter task. For that reason, NVMe driver uses task-work infra for > >>>>>> that ioctl-specific update. Since task-work is not exported, it cannot > >>>>>> be referenced when nvme is compiled as a module. Therefore, one of the > >>>>>> patch exports task-work API. > >>>>>> > >>>>>> Here goes example of usage (pseudo-code). > >>>>>> Actual nvme-cli source, modified to issue all ioctls via this opcode > >>>>>> is present at- > >>>>>> https://github.com/joshkan/nvme-cli/commit/a008a733f24ab5593e7874cfbc69ee04e88068c5 > >>>>> > >>>>> see https://git.kernel.dk/cgit/linux-block/log/?h=io_uring-fops > >>>>> > >>>>> Looks like good time to bring that branch/discussion back > >>>> > >>>> a bit more context: > >>>> https://github.com/axboe/liburing/issues/270 > >>> > >>> Thanks, it looked good. It seems key differences (compared to > >>> uring-patch that I posted) are - > >>> 1. using file-operation instead of block-dev operation. > >> > >> Right, it's meant to span wider than just block devices. > >> > >>> 2. repurpose the sqe memory for ioctl-cmd. If an application does > >>> ioctl with <=40 bytes of cmd, it does not have to allocate ioctl-cmd. > >>> That's nifty. We still need to support passing larger-cmd (e.g. > >>> nvme-passthru ioctl takes 72 bytes) but that shouldn't get too > >>> difficult I suppose. > >> > >> It's actually 48 bytes in the as-posted version, and I've bumped it to > >> 56 bytes in the latest branch. So not quite enough for everything, > >> nothing ever will be, but should work for a lot of cases without > >> requiring per-command allocations just for the actual command. > > > > Agreed. But if I got it right, you are open to support both in-the-sqe > > command (<= 56 bytes) and out-of-sqe command (> 56 bytes) with this > > interface. > > Driver processing the ioctl can fetch the cmd from user-space in one > > case (as it does now), and skips in another. > > Your out-of-seq command would be none of io_urings business, outside of > the fact that we'd need to ensure it's stable if we need to postpone > it. So yes, that would be fine, it just means your actual command is > passed in as a pointer, and you would be responsible for copying it > in for execution > > We're going to need something to handle postponing, and something > for ensuring that eg cancelations free the allocated memory. I have few doubts about allocation/postponing. Are you referring to uring allocating memory for this case, similar to the way "req->async_data" is managed for few other opcodes? Or can it (i.e. larger cmd) remain a user-space pointer, and the underlying driver fetches the command in. If submission context changes (for sqo/io-wq case), uring seemed to apply context-grabbing techniques to make that work. > >>> And for some ioctls, driver may still need to use task-work to update > >>> the user-space pointers (embedded in uring/ioctl cmd) during > >>> completion. > >>> > >>> @Jens - will it be fine if I start looking at plumbing nvme-part of > >>> this series on top of your work? > >> > >> Sure, go ahead. Just beware that things are still changing, so you might > >> have to adapt it a few times. It's still early days, but I do think > >> that's the way forward in providing controlled access to what is > >> basically async ioctls. > > > > Sounds good, I will start with the latest branch that you posted. Thanks. > > It's io_uring-fops.v2 for now, use that one. Moved to v3 now. nvme_user_io is 48 bytes, while nvme passthrough requires 72 or 80 bytes (passthru with 64 bit result). The block_uring_cmd has 32 bytes of available space. If NVMe defines its own "nvme_uring_cmd" (which can be used for nvme char interface) that will buy some more space, but still won't be enough for passthru command. So I am looking at adding support for large-cmd in uring. And felt the need to clear those doubts I mentioned above. Thanks