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=-15.1 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 13F23C433E0 for ; Tue, 9 Feb 2021 16:10:07 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id 7343F64EAA for ; Tue, 9 Feb 2021 16:10:06 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7343F64EAA Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:35572 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1l9VaX-0007Dn-DB for qemu-devel@archiver.kernel.org; Tue, 09 Feb 2021 11:10:05 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:48418) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1l9VZX-0006fj-AU for qemu-devel@nongnu.org; Tue, 09 Feb 2021 11:09:03 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:25522) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1l9VZU-0004gd-Rx for qemu-devel@nongnu.org; Tue, 09 Feb 2021 11:09:03 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1612886939; 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=OOEEKEK39d2ihbyxoXx+rvmNog7OeWTulrGZkTKnO1A=; b=gGcKqaXs4vt7mChvBw0NPul/NsRojXO/kGH50is/ipBkaBeewKDtTcdGfREpNWkFW5qdR+ SiI2ZeGS+b9fGU1MFAD+LSFv4ZtiPXIx0i8jcVdCQRYZvaewpCYEYfAqdDs0UCzq/jCZPU n/vNM3RtjfsINJGX/BI5bEQXxs+sk2M= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-233-G1uZSGguMtaQ3FER19vwyQ-1; Tue, 09 Feb 2021 11:08:54 -0500 X-MC-Unique: G1uZSGguMtaQ3FER19vwyQ-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 07B30192D786; Tue, 9 Feb 2021 16:08:53 +0000 (UTC) Received: from localhost (ovpn-114-98.ams2.redhat.com [10.36.114.98]) by smtp.corp.redhat.com (Postfix) with ESMTP id A4E395D745; Tue, 9 Feb 2021 16:08:52 +0000 (UTC) Date: Tue, 9 Feb 2021 16:08:51 +0000 From: "Richard W.M. Jones" To: Eric Blake Subject: Re: [PATCH v3 1/2] qemu-nbd: Use SOMAXCONN for socket listen() backlog Message-ID: <20210209160851.GA30079@redhat.com> References: <20210209152759.209074-1-eblake@redhat.com> <20210209152759.209074-2-eblake@redhat.com> MIME-Version: 1.0 In-Reply-To: <20210209152759.209074-2-eblake@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=rjones@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=216.205.24.124; envelope-from=rjones@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -33 X-Spam_score: -3.4 X-Spam_bar: --- X-Spam_report: (-3.4 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.57, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , berrange@redhat.com, qemu-block@nongnu.org, qemu-devel@nongnu.org, qemu-stable@nongnu.org, nsoffer@redhat.com, Max Reitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, Feb 09, 2021 at 09:27:58AM -0600, Eric Blake wrote: > Our default of a backlog of 1 connection is rather puny; it gets in > the way when we are explicitly allowing multiple clients (such as > qemu-nbd -e N [--shared], or nbd-server-start with its default > "max-connections":0 for unlimited), but is even a problem when we > stick to qemu-nbd's default of only 1 active client but use -t > [--persistent] where a second client can start using the server once > the first finishes. While the effects are less noticeable on TCP > sockets (since the client can poll() to learn when the server is ready > again), it is definitely observable on Unix sockets, where on Unix, a > client will fail with EAGAIN and no recourse but to sleep an arbitrary > amount of time before retrying if the server backlog is already full. > > Since QMP nbd-server-start is always persistent, it now always > requests a backlog of SOMAXCONN; meanwhile, qemu-nbd will request > SOMAXCONN if persistent, otherwise its backlog should be based on the > expected number of clients. > > See https://bugzilla.redhat.com/1925045 for a demonstration of where > our low backlog prevents libnbd from connecting as many parallel > clients as it wants. > > Reported-by: Richard W.M. Jones > Signed-off-by: Eric Blake > CC: qemu-stable@nongnu.org > --- > blockdev-nbd.c | 7 ++++++- > qemu-nbd.c | 10 +++++++++- > 2 files changed, 15 insertions(+), 2 deletions(-) > > diff --git a/blockdev-nbd.c b/blockdev-nbd.c > index d8443d235b73..b264620b98d8 100644 > --- a/blockdev-nbd.c > +++ b/blockdev-nbd.c > @@ -134,7 +134,12 @@ void nbd_server_start(SocketAddress *addr, const char *tls_creds, > qio_net_listener_set_name(nbd_server->listener, > "nbd-listener"); > > - if (qio_net_listener_open_sync(nbd_server->listener, addr, 1, errp) < 0) { > + /* > + * Because this server is persistent, a backlog of SOMAXCONN is > + * better than trying to size it to max_connections. > + */ > + if (qio_net_listener_open_sync(nbd_server->listener, addr, SOMAXCONN, > + errp) < 0) { > goto error; > } > > diff --git a/qemu-nbd.c b/qemu-nbd.c > index 608c63e82a25..1a340ea4858d 100644 > --- a/qemu-nbd.c > +++ b/qemu-nbd.c > @@ -964,8 +964,16 @@ int main(int argc, char **argv) > > server = qio_net_listener_new(); > if (socket_activation == 0) { > + int backlog; > + > + if (persistent) { > + backlog = SOMAXCONN; > + } else { > + backlog = MIN(shared, SOMAXCONN); > + } > saddr = nbd_build_socket_address(sockpath, bindto, port); > - if (qio_net_listener_open_sync(server, saddr, 1, &local_err) < 0) { > + if (qio_net_listener_open_sync(server, saddr, backlog, > + &local_err) < 0) { > object_unref(OBJECT(server)); > error_report_err(local_err); > exit(EXIT_FAILURE); Works fine here, so: Tested-by: Richard W.M. Jones Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com Fedora Windows cross-compiler. Compile Windows programs, test, and build Windows installers. Over 100 libraries supported. http://fedoraproject.org/wiki/MinGW