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 Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 64CBFC7115A for ; Fri, 18 Aug 2023 15:24:42 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qX1Kx-0005vz-Dd; Fri, 18 Aug 2023 11:24:31 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qX1Kv-0005vG-GN for qemu-devel@nongnu.org; Fri, 18 Aug 2023 11:24:29 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qX1Kt-0002xF-CM for qemu-devel@nongnu.org; Fri, 18 Aug 2023 11:24:29 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1692372266; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=GbAPyh1fMnlkSKZoCerNUTFiu60FRKPTbkNGlRZnHrg=; b=VTXJMJzb9RWHqytNk1+ZHwrAP4RwIKC3Ia2jI3eciPlsaqf8kDhTESfsWqfzjWM2OQYoxB jstbiUCYIVDj2FZLISRTMgZAg7rEv1/q6GGAriofLokyh8GEv4qeUelZvsdE1z42VF7Eem BaLnKazrZjoIX5d627Uwg2XIQwUCHBQ= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-589-pjvH6wciNH-2WuMCQWYw5w-1; Fri, 18 Aug 2023 11:24:24 -0400 X-MC-Unique: pjvH6wciNH-2WuMCQWYw5w-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 7EB43101A53C; Fri, 18 Aug 2023 15:24:24 +0000 (UTC) Received: from redhat.com (unknown [10.39.192.160]) by smtp.corp.redhat.com (Postfix) with ESMTPS id C4AF3492C13; Fri, 18 Aug 2023 15:24:23 +0000 (UTC) Date: Fri, 18 Aug 2023 17:24:22 +0200 From: Kevin Wolf To: Stefan Hajnoczi Cc: qemu-devel@nongnu.org, Hanna Reitz , qemu-block@nongnu.org Subject: Re: [PATCH 0/2] block-backend: process I/O in the current AioContext Message-ID: References: <20230815160521.3357063-1-stefanha@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230815160521.3357063-1-stefanha@redhat.com> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.10 Received-SPF: pass client-ip=170.10.129.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Am 15.08.2023 um 18:05 hat Stefan Hajnoczi geschrieben: > Switch blk_aio_*() APIs over to multi-queue by using > qemu_get_current_aio_context() instead of blk_get_aio_context(). This change > will allow devices to process I/O in multiple IOThreads in the future. Both code paths still use blk_aio_em_aiocb_info, which is: static AioContext *blk_aio_em_aiocb_get_aio_context(BlockAIOCB *acb_) { BlkAioEmAIOCB *acb = container_of(acb_, BlkAioEmAIOCB, common); return blk_get_aio_context(acb->rwco.blk); } static const AIOCBInfo blk_aio_em_aiocb_info = { .aiocb_size = sizeof(BlkAioEmAIOCB), .get_aio_context = blk_aio_em_aiocb_get_aio_context, }; .get_aio_context() is called by bdrv_aio_cancel(), which already looks wrong before this patch because in theory it can end up polling the AioContext of a different thread. After this patch, .get_aio_context() doesn't even necessarily return the AioContext that runs the request any more. The only thing that might save us is that I can't find any device that both supports iothreads and calls bdrv_aio_cancel(). But we shouldn't rely on that. Maybe the solution is to just remove .get_aio_context altogether and use AIO_WAIT_WHILE(NULL, ...) in bdrv_aio_cancel(). Kevin