From patchwork Fri Mar 8 01:47:39 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Ben Pfaff X-Patchwork-Id: 1053332 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Authentication-Results: ozlabs.org; spf=pass (mailfrom) smtp.mailfrom=openvswitch.org (client-ip=140.211.169.12; helo=mail.linuxfoundation.org; envelope-from=ovs-dev-bounces@openvswitch.org; receiver=) Authentication-Results: ozlabs.org; dmarc=none (p=none dis=none) header.from=ovn.org Received: from mail.linuxfoundation.org (mail.linuxfoundation.org [140.211.169.12]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 44Fr3x3glPz9s9N for ; Fri, 8 Mar 2019 12:47:56 +1100 (AEDT) Received: from mail.linux-foundation.org (localhost [127.0.0.1]) by mail.linuxfoundation.org (Postfix) with ESMTP id EAE25CBC0; Fri, 8 Mar 2019 01:47:51 +0000 (UTC) X-Original-To: dev@openvswitch.org Delivered-To: ovs-dev@mail.linuxfoundation.org Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id 53100C77A for ; Fri, 8 Mar 2019 01:47:51 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from relay9-d.mail.gandi.net (relay9-d.mail.gandi.net [217.70.183.199]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id AC57BD3 for ; Fri, 8 Mar 2019 01:47:50 +0000 (UTC) X-Originating-IP: 75.54.222.30 Received: from sigill.attlocal.net (75-54-222-30.lightspeed.rdcyca.sbcglobal.net [75.54.222.30]) (Authenticated sender: blp@ovn.org) by relay9-d.mail.gandi.net (Postfix) with ESMTPSA id 4D3FBFF802; Fri, 8 Mar 2019 01:47:46 +0000 (UTC) From: Ben Pfaff To: dev@openvswitch.org Date: Thu, 7 Mar 2019 17:47:39 -0800 Message-Id: <20190308014739.26997-1-blp@ovn.org> X-Mailer: git-send-email 2.20.1 MIME-Version: 1.0 X-Spam-Status: No, score=-2.6 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_LOW autolearn=ham version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on smtp1.linux-foundation.org Cc: Ben Pfaff Subject: [ovs-dev] [PATCH] faq: Explain why select groups don't sort out packets evenly. X-BeenThere: ovs-dev@openvswitch.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: ovs-dev-bounces@openvswitch.org Errors-To: ovs-dev-bounces@openvswitch.org This keeps coming up. Signed-off-by: Ben Pfaff Signed-off-by: Ben Pfaff > Acked-by: Alin Gabriel Serdean > --- Documentation/faq/openflow.rst | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/Documentation/faq/openflow.rst b/Documentation/faq/openflow.rst index 4a20255daf21..561d793a6692 100644 --- a/Documentation/faq/openflow.rst +++ b/Documentation/faq/openflow.rst @@ -478,6 +478,22 @@ Q: How does OVS divide flows among buckets in an OpenFlow "select" group? Documentation/group-selection-method-property.txt in the Open vSwitch source tree. (OpenFlow 1.5 support in Open vSwitch is still experimental.) +Q: An OpenFlow "select" group isn't dividing packets evenly among the buckets. + + A: When a packet passes through a "select" group, Open vSwitch hashes a + subset of the fields in the packet, then it maps the hash value to a + bucket. This means that packets whose hashed fields are the same will + always go to the same bucket[*]. More specifically, if you test with a + single traffic flow, only one bucket will receive any traffic[**]. + Furthermore, statistics and probability mean that testing with a small + number of flows may still yield an uneven distribution. + + [*] Unless its bucket has a watch port or group whose liveness changes + during the test. + + [**] Unless the hash includes fields that vary within a traffic flow, such + as tcp_flags. + Q: I added a flow to accept packets on VLAN 123 and output them on VLAN 456, like so::