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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham 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 69A97C43387 for ; Wed, 2 Jan 2019 19:11:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 35684218FC for ; Wed, 2 Jan 2019 19:11:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729020AbfABTLp (ORCPT ); Wed, 2 Jan 2019 14:11:45 -0500 Received: from mx1.redhat.com ([209.132.183.28]:49538 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729016AbfABTLp (ORCPT ); Wed, 2 Jan 2019 14:11:45 -0500 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 36C54D963D; Wed, 2 Jan 2019 19:11:45 +0000 (UTC) Received: from segfault.boston.devel.redhat.com (segfault.boston.devel.redhat.com [10.19.60.26]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 63B0B5C207; Wed, 2 Jan 2019 19:11:44 +0000 (UTC) From: Jeff Moyer To: Jens Axboe Cc: linux-fsdevel@vger.kernel.org, linux-aio@kvack.org, linux-block@vger.kernel.org, hch@lst.de, viro@zeniv.linux.org.uk Subject: Re: [PATCH 16/22] aio: add support for submission/completion rings References: <20181221192236.12866-1-axboe@kernel.dk> <20181221192236.12866-17-axboe@kernel.dk> X-PGP-KeyID: 1F78E1B4 X-PGP-CertKey: F6FE 280D 8293 F72C 65FD 5A58 1FF8 A7CA 1F78 E1B4 Date: Wed, 02 Jan 2019 14:11:43 -0500 In-Reply-To: <20181221192236.12866-17-axboe@kernel.dk> (Jens Axboe's message of "Fri, 21 Dec 2018 12:22:30 -0700") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Wed, 02 Jan 2019 19:11:45 +0000 (UTC) Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org Jens Axboe writes: > The submission queue (SQ) and completion queue (CQ) rings are shared > between the application and the kernel. This eliminates the need to > copy data back and forth to submit and complete IO. We use the same > structures as the old aio interface. The SQ rings are indexes into a > struct iocb array, like we would submit through io_submit(), and the > CQ rings are struct io_event, like we would pass in (and copy back) > from io_getevents(). > > A new system call is added for this, io_ring_enter(). This system call > submits IO that is stored in the SQ ring, and/or completes IO and stores > the results in the CQ ring. Hence it's possible to both complete and > submit IO in a single system call. > > For IRQ driven IO, an application only needs to enter the kernel for > completions if it wants to wait for them to occur. It looks like the memory for the submission and completion queues is not migratable (scq rings are non-migratory! [1]). Maybe you should use the aio pseudofs for allocations, like is done with the original aio ring. I realize that would change the api... -Jeff [1] https://www.youtube.com/watch?v=liIlW-ovx0Y