From patchwork Wed Jul 12 16:20:09 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jens Axboe X-Patchwork-Id: 13310724 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id BF85DEB64DA for ; Wed, 12 Jul 2023 16:21:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232035AbjGLQVn (ORCPT ); Wed, 12 Jul 2023 12:21:43 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51408 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231791AbjGLQV3 (ORCPT ); Wed, 12 Jul 2023 12:21:29 -0400 Received: from mail-io1-xd33.google.com (mail-io1-xd33.google.com [IPv6:2607:f8b0:4864:20::d33]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 127C12715 for ; Wed, 12 Jul 2023 09:20:24 -0700 (PDT) Received: by mail-io1-xd33.google.com with SMTP id ca18e2360f4ac-78706966220so32743239f.1 for ; Wed, 12 Jul 2023 09:20:24 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel-dk.20221208.gappssmtp.com; s=20221208; t=1689178822; x=1691770822; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=GB+TVOcEAGohMo/9qjG0tcL6VxFJuBiixHc0IQwbD98=; b=JqNSJM5QCDkw+R1ww+DDY6XYeGWUbAsCxQxhbbvdBaY2g7Yo9mq1Utaza/2CKVSM8B yDUYnnK6aVmrxP9r7gx+AZAaNJ1K4hxf2piEFU+6mlK1+eDms+kicmruEfTrHp0ik2Tt Vm+ktb+O8l708FmhVBKRZMaPK84pe3A7EU5PKUaNKk1VKGdOjQpM1eH+d+KC1BnPFvt6 LUxcTf90msPzRfcZqu0dh/LdCvPF+veHMiBnP5SgE1py/1HsKWqogpgveuIjiLxf1NZq M15munixc7UyORn1PlwYnauNOx1mIl1XABPGBcoCcjS+zit6CSyO2n9iVqMNJ3wR1riJ bYfA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1689178822; x=1691770822; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=GB+TVOcEAGohMo/9qjG0tcL6VxFJuBiixHc0IQwbD98=; b=TmNdP4W1o0tnIe37Jc8NLFUYJTNVQa1fQwt4wJikMTmcATeFhbuG4W0f6XvhZ3KTcU 5m199o02vyI4EPQXJnAX/pLZ5Z8EvRSy3Ks8nzWTE2nBbsjZzZnBnJcS55iP+94Z7SQz dyDWCE/RzVlQ1UJ/VsVkrBRGKPgQd9aCGGgYTggkFxp/yBfzgz8Jk/0ah6jKA52D8UmH tJSIDtCjxGgFW9prZJx0s66evqfLGu24ebYExEHNN83u97ZawsbcSX5IBEbqzTU/x7rC v0D3WlUZKhzsGSuFPhUK3iyVRgKrnKVo4aYRUu0OlvOjhr1I5QXt0OUX5LN9WiU6kzU9 fdNA== X-Gm-Message-State: ABy/qLY8FxqrBBxcdDZcV5F1dzhWBvB12FSnFVSgE3OVnaxNh9AieXXN smnviUVHKJmmed7A279L1iXeTnOqm5HMtJcprGE= X-Google-Smtp-Source: APBJJlHtuORB22XquZ9IWPiPN1Pbeftomu0zTo5Kw9NMbEPkmyQCmhyPA1/w87Jx09AggSZc60s2vQ== X-Received: by 2002:a6b:1489:0:b0:780:cde6:3e22 with SMTP id 131-20020a6b1489000000b00780cde63e22mr18243438iou.0.1689178822177; Wed, 12 Jul 2023 09:20:22 -0700 (PDT) Received: from localhost.localdomain ([96.43.243.2]) by smtp.gmail.com with ESMTPSA id x24-20020a029718000000b0042aec33bc26sm1328775jai.18.2023.07.12.09.20.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 12 Jul 2023 09:20:21 -0700 (PDT) From: Jens Axboe To: io-uring@vger.kernel.org, linux-kernel@vger.kernel.org Cc: tglx@linutronix.de, mingo@redhat.com, peterz@infradead.org, andres@anarazel.de Subject: [PATCHSET v2 0/8] Add io_uring futex/futexv support Date: Wed, 12 Jul 2023 10:20:09 -0600 Message-Id: <20230712162017.391843-1-axboe@kernel.dk> X-Mailer: git-send-email 2.40.1 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org Hi, This patchset adds support for first futex wake and wait, and then futexv. Patches 1..3 are just prep patches, patch 4 adds the wait and wake support for io_uring, and then patches 5..7 are again prep patches to end up with futexv support in patch 8. For both wait/wake/waitv, we support the bitset variant, as the "normal" variants can be easily implemented on top of that. PI and requeue are not supported through io_uring, just the above mentioned parts. This may change in the future, but in the spirit of keeping this small (and based on what people have been asking for), this is what we currently have. When I did these patches, I forgot that Pavel had previously posted a futex variant for io_uring. The major thing that had been holding me back from people asking about futexes and io_uring, is that I wanted to do this what I consider the right way - no usage of io-wq or thread offload, an actually async implementation that is efficient to use and don't rely on a blocking thread for futex wait/waitv. This is what this patchset attempts to do, while being minimally invasive on the futex side. I believe the diffstat reflects that. As far as I can recall, the first request for futex support with io_uring came from Andres Freund, working on postgres. His aio rework of postgres was one of the early adopters of io_uring, and futex support was a natural extension for that. This is relevant from both a usability point of view, as well as for effiency and performance. In Andres's words, for the former: "Futex wait support in io_uring makes it a lot easier to avoid deadlocks in concurrent programs that have their own buffer pool: Obviously pages in the application buffer pool have to be locked during IO. If the initiator of IO A needs to wait for a held lock B, the holder of lock B might wait for the IO A to complete. The ability to wait for a lock and IO completions at the same time provides an efficient way to avoid such deadlocks." and in terms of effiency, even without unlocking the full potential yet, Andres says: "Futex wake support in io_uring is useful because it allows for more efficient directed wakeups. For some "locks" postgres has queues implemented in userspace, with wakeup logic that cannot easily be implemented with FUTEX_WAKE_BITSET on a single "futex word" (imagine waiting for journal flushes to have completed up to a certain point). Thus a "lock release" sometimes need to wake up many processes in a row. A quick-and-dirty conversion to doing these wakeups via io_uring lead to a 3% throughput increase, with 12% fewer context switches, albeit in a fairly extreme workload." Some basic io_uring futex support and test cases are available in the liburing 'futex' branch: https://git.kernel.dk/cgit/liburing/log/?h=futex testing all of the variants. I originally wrote this code about a month ago and Andres has been using it with postgres, and I'm not aware of any bugs in it. That's not to say it's perfect, obviously, and I welcome some feedback so we can move this forward and hash out any potential issues. include/linux/io_uring_types.h | 3 + include/uapi/linux/io_uring.h | 4 + io_uring/Makefile | 4 +- io_uring/cancel.c | 5 + io_uring/cancel.h | 4 + io_uring/futex.c | 376 +++++++++++++++++++++++++++++++++ io_uring/futex.h | 36 ++++ io_uring/io_uring.c | 5 + io_uring/opdef.c | 35 ++- kernel/futex/futex.h | 33 +++ kernel/futex/requeue.c | 3 +- kernel/futex/syscalls.c | 27 ++- kernel/futex/waitwake.c | 49 +++-- 13 files changed, 548 insertions(+), 36 deletions(-) You can also find the code here: https://git.kernel.dk/cgit/linux/log/?h=io_uring-futex V2: - Abstract out __futex_wake_mark() helper. Use it both in the futex and io_uring code. This also fixes a missing WARN_ON on the io_uring side. - Have futex_op_to_flags() unconditionally clear flags to zero rather than do that in both callers. - Remove comment on needing to open-code futex_queue(), and associated hunk doing that. This was a leftover from an earlier version. - Expand the commit message logs in various patches.