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=-13.6 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 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 AEC11C433E0 for ; Tue, 9 Feb 2021 15:31:06 +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 E6A8164EB8 for ; Tue, 9 Feb 2021 15:31:05 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E6A8164EB8 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]:37492 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1l9Uym-00070r-Ot for qemu-devel@archiver.kernel.org; Tue, 09 Feb 2021 10:31:04 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:38170) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1l9Uw0-0005R4-Rw for qemu-devel@nongnu.org; Tue, 09 Feb 2021 10:28:12 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:21116) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1l9Uvx-0003rT-Ct for qemu-devel@nongnu.org; Tue, 09 Feb 2021 10:28:12 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1612884488; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=lDFDY261wZp/LgJ4CqOOWZztGEFUiZcwKglFLBxC7p0=; b=S6CF8L3glKQpwGtyeD/Iu+tRU12h4txPruMsGDhqIjYFDKLWVxZMj9l/wXyNuvRpAtRqug if4w19Min+levdaTWsrrKLaiQMZTd0V91vvEjv1BeaI2EBlsjD0NV++V84gF4OB2nn84pq ViQAv29s162s3YQljmm2SXjwGmY2VuM= 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-289-lgVL6X03PwKyW4ILcWGmYA-1; Tue, 09 Feb 2021 10:28:06 -0500 X-MC-Unique: lgVL6X03PwKyW4ILcWGmYA-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 DE658107ACE6; Tue, 9 Feb 2021 15:28:04 +0000 (UTC) Received: from blue.redhat.com (ovpn-114-150.phx2.redhat.com [10.3.114.150]) by smtp.corp.redhat.com (Postfix) with ESMTP id E59D95D730; Tue, 9 Feb 2021 15:28:01 +0000 (UTC) From: Eric Blake To: qemu-devel@nongnu.org Subject: [PATCH v3 1/2] qemu-nbd: Use SOMAXCONN for socket listen() backlog Date: Tue, 9 Feb 2021 09:27:58 -0600 Message-Id: <20210209152759.209074-2-eblake@redhat.com> In-Reply-To: <20210209152759.209074-1-eblake@redhat.com> References: <20210209152759.209074-1-eblake@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=eblake@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset="US-ASCII" Received-SPF: pass client-ip=216.205.24.124; envelope-from=eblake@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=unavailable 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, rjones@redhat.com, qemu-stable@nongnu.org, nsoffer@redhat.com, Max Reitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 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); -- 2.30.0