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=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 2B2A3C47082 for ; Mon, 7 Jun 2021 18:52:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0C9AB61139 for ; Mon, 7 Jun 2021 18:52:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231287AbhFGSye (ORCPT ); Mon, 7 Jun 2021 14:54:34 -0400 Received: from mail-ej1-f42.google.com ([209.85.218.42]:35406 "EHLO mail-ej1-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230463AbhFGSyd (ORCPT ); Mon, 7 Jun 2021 14:54:33 -0400 Received: by mail-ej1-f42.google.com with SMTP id h24so28424959ejy.2 for ; Mon, 07 Jun 2021 11:52:31 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nametag.social; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=ScXrC8JzROe4oik0nKr4Zt97X1eNIvPR3vNcHFbWFVw=; b=zNYJK3b0Nb8HpGi/aABY5z2iapsdx7yAQtFWXWDFPJbKUfJQRiCc4K3VvQzVgBNVV7 WmcbojERHJ6iCdEs9d2RqP7whPvdiFbmY/hEO9hD7unbLU1FJCZjPcn0fa3AXh17EJvt n1bDhfDzsCeih8kV5nUptWol/9UYaSzIPzwsjT6P4otB7wjamQ/cdTSrNoBOxdMm2TCw nzGkMLQXg75dYNSIbXaUv9J7X2nnp+CO2+Xss/4obDx7I5daox9uJ0pE142qL5X+MKzy svxWHQMtvw3F2N1yxMEHFRXR17tTdive8JPi5xi9sSzu7+c5DTerRO422bt36YGuJTMy v2Qg== 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=ScXrC8JzROe4oik0nKr4Zt97X1eNIvPR3vNcHFbWFVw=; b=IzXrssreKZ8azK10eLvQ4jYrgtTT8PeDDKc9lW/bSTnsmzEbYKVHg9dw0YD9NeI8ML LTzh7hJFr++1mBFOzTfEOoelhU/B0l2uwUIab2gJN1ALH2IBUKbZcxI7ay7UoyCA0Rz/ cgzWkgu3zEfr9THTeIpFvuB+B7Pvhjo/c90WcS98HqHyEZJO8FYhwS80zXMZCxOB5ivW TrqRL/9TXNrgtKvtXzwKLDVXrBBPnh5eXYYTyRU4WgKDwyUYfL7GFX+qXR834ObKTJKx zNFmXHwGJZ0/b9qtHYiBCQ6ab1w8xJFRuFWoQ8jEYQf/nmwiBAqHavVnLQB3KIFPcf2m R0Yw== X-Gm-Message-State: AOAM533szgFLOTMBXHZ+jd08pgo/5Q6ZritJuptO3zSgeWdcZslIa569 5aBFnzvV4J34BpxlFY6w1Ww6qYqUmbUJWTOfVV1pYA== X-Google-Smtp-Source: ABdhPJzGcWFGWbIbsY89L7lxhJBfNHplKZCa8ow1UNqgMe/NUtgdE/5lRdP7v1aSFE5Cm6Z9w/5qLJg6WT/lTXHQNYY= X-Received: by 2002:a17:906:c010:: with SMTP id e16mr19541841ejz.214.1623091890615; Mon, 07 Jun 2021 11:51:30 -0700 (PDT) MIME-Version: 1.0 References: <23168ac0-0f05-3cd7-90dc-08855dd275b2@gmail.com> In-Reply-To: <23168ac0-0f05-3cd7-90dc-08855dd275b2@gmail.com> From: Victor Stewart Date: Mon, 7 Jun 2021 14:51:19 -0400 Message-ID: Subject: Re: io_uring: BPF controlled I/O To: Pavel Begunkov Cc: io-uring , Jens Axboe , "linux-block@vger.kernel.org" , LKML , bpf , lsf-pc@lists.linux-foundation.org Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Sat, Jun 5, 2021 at 5:09 AM Pavel Begunkov wrote: > > One of the core ideas behind io_uring is passing requests via memory > shared b/w the userspace and the kernel, a.k.a. queues or rings. That > serves a purpose of reducing number of context switches or bypassing > them, but the userspace is responsible for controlling the flow, > reaping and processing completions (a.k.a. Completion Queue Entry, CQE), > and submitting new requests, adding extra context switches even if there > is not much work to do. A simple illustration is read(open()), where > io_uring is unable to propagate the returned fd to the read, with more > cases piling up. > > The big picture idea stays the same since last year, to give out some > of this control to BPF, allow it to check results of completed requests, > manipulate memory if needed and submit new requests. Apart from being > just a glue between two requests, it might even offer more flexibility > like keeping a QD, doing reduce/broadcast and so on. > > The prototype [1,2] is in a good shape but some work need to be done. > However, the main concern is getting an understanding what features and > functionality have to be added to be flexible enough. Various toy > examples can be found at [3] ([1] includes an overview of cases). > > Discussion points: > - Use cases, feature requests, benchmarking hi Pavel, coincidentally i'm tossing around in my mind at the moment an idea for offloading the PING/PONG of a QUIC server/client into the kernel via eBPF. problem being, being that QUIC is userspace run transport and that NAT-ed UDP mappings can't be expected to stay open longer than 30 seconds, QUIC applications bare a large cost of context switching wake-up to conduct connection lifetime maintenance... especially when managing a large number of mostly idle long lived connections. so offloading this maintenance service into the kernel would be a great efficiency boon. the main impediment is that access to the kernel crypto libraries isn't currently possible from eBPF. that said, connection wide crypto offload into the NIC is a frequently mentioned subject in QUIC circles, so one could argue better to allocate the time to NIC crypto offload and then simply conduct this PING/PONG offload in plain text. CQEs would provide a great way for the offloaded service to be able to wake up the application when it's input is required. anyway food for thought. Victor > - Userspace programming model, code reuse (e.g. liburing) > - BPF-BPF and userspace-BPF synchronisation. There is > CQE based notification approach and plans (see design > notes), however need to discuss what else might be > needed. > - Do we need more contexts passed apart from user_data? > e.g. specifying a BPF map/array/etc fd io_uring requests? > - Userspace atomics and efficiency of userspace reads/writes. If > proved to be not performant enough there are potential ways to take > on it, e.g. inlining, having it in BPF ISA, and pre-verifying > userspace pointers. > > [1] https://lore.kernel.org/io-uring/a83f147b-ea9d-e693-a2e9-c6ce16659749@gmail.com/T/#m31d0a2ac6e2213f912a200f5e8d88bd74f81406b > [2] https://github.com/isilence/linux/tree/ebpf_v2 > [3] https://github.com/isilence/liburing/tree/ebpf_v2/examples/bpf > > > ----------------------------------------------------------------------- > Design notes: > > Instead of basing it on hooks it adds support of a new type of io_uring > requests as it gives a better control and let's to reuse internal > infrastructure. These requests run a new type of io_uring BPF programs > wired with a bunch of new helpers for submitting requests and dealing > with CQEs, are allowed to read/write userspace memory in virtue of a > recently added sleepable BPF feature. and also provided with a token > (generic io_uring token, aka user_data, specified at submission and > returned in an CQE), which may be used to pass a userspace pointer used > as a context. > > Besides running BPF programs, they are able to request waiting. > Currently it supports CQ waiting for a number of completions, but others > might be added and/or needed, e.g. futex and/or requeueing the current > BPF request onto an io_uring request/link being submitted. That hides > the overhead of creating BPF requests by keeping them alive and > invoking multiple times. > > Another big chunk solved is figuring out a good way of feeding CQEs > (potentially many) to a BPF program. The current approach > is to enable multiple completion queues (CQ), and specify for each > request to which one steer its CQE, so all the synchronisation > is in control of the userspace. For instance, there may be a separate > CQ per each in-flight BPF request, and they can work with their own > queues and send an CQE to the main CQ so notifying the userspace. > It also opens up a notification-like sync through CQE posting to > neighbours' CQs. > > > -- > Pavel Begunkov