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 DE815C369D5 for ; Mon, 28 Apr 2025 19:29:26 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1u9UAG-0004YG-9K; Mon, 28 Apr 2025 15:29:16 -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 1u9UAD-0004Wv-Ew for qemu-devel@nongnu.org; Mon, 28 Apr 2025 15:29:13 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1u9UAB-0008SA-Oq for qemu-devel@nongnu.org; Mon, 28 Apr 2025 15:29:13 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1745868548; 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=gll9Rxp5n2BPvksSyTd2/o8pxifoanyEEFX8FSjf7yE=; b=TKbBd39NDxv/lpJYllQ8O5k4QB4rU+WhK9mVr4DGGiBQubsVRs6jeYV4dyNvrp13drsiRj F0xocAh1xMKFsNfMhtxu3mL2zKyuD3xRYQnRh+V52RMZFQKam4ZDWZ6xm8d5VNQ8dyGBUa ssz+uaqOq1pPiuto18gLR4jUvCFKiyY= Received: from mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-15-9K2gcXYnOgik3y1vLsmcew-1; Mon, 28 Apr 2025 15:27:58 -0400 X-MC-Unique: 9K2gcXYnOgik3y1vLsmcew-1 X-Mimecast-MFC-AGG-ID: 9K2gcXYnOgik3y1vLsmcew_1745868477 Received: from mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.40]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id D7E8D180087A; Mon, 28 Apr 2025 19:27:55 +0000 (UTC) Received: from localhost (unknown [10.42.28.3]) by mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 0B8E419560A3; Mon, 28 Apr 2025 19:27:54 +0000 (UTC) Date: Mon, 28 Apr 2025 20:27:54 +0100 From: "Richard W.M. Jones" To: Eric Blake Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org, Vladimir Sementsov-Ogievskiy , Kevin Wolf , Hanna Reitz Subject: Re: [PATCH v2 4/4] nbd: Enable multi-conn using round-robin Message-ID: <20250428192754.GF1450@redhat.com> References: <20250428185246.492388-6-eblake@redhat.com> <20250428185246.492388-10-eblake@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250428185246.492388-10-eblake@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Scanned-By: MIMEDefang 3.0 on 10.30.177.40 Received-SPF: pass client-ip=170.10.133.124; envelope-from=rjones@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -25 X-Spam_score: -2.6 X-Spam_bar: -- X-Spam_report: (-2.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.484, 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_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable 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 On Mon, Apr 28, 2025 at 01:46:47PM -0500, Eric Blake wrote: [...] This all looks similar to when I posted it before. However I noted a couple of problems ... > (XXX) The strategy here is very naive. Firstly if you were going to > open them, you'd probably want to open them in parallel. Secondly it > would make sense to delay opening until multiple parallel requests are > seen (perhaps above some threshold), so that simple or shortlived NBD > operations do not require multiple connections to be made. > (XXX) This uses a naive round-robin approach which could be improved. > For example we could look at how many requests are in flight and > assign operations to the connections with fewest. Or we could try to > estimate (based on size of requests outstanding) the load on each > connection. But this implementation doesn't do any of that. Plus there was a third rather more fundamental problem that apparently I didn't write about. That is that connections were serialised on a single thread (called from many coroutines). This bottleneck meant that there wasn't very much advantage to multi-conn, compared to what we get in libnbd / nbdcopy. Are these fixed / planned to be fixed, especially the third? Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-top is 'top' for virtual machines. Tiny program with many powerful monitoring features, net stats, disk stats, logging, etc. http://people.redhat.com/~rjones/virt-top