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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D46A8C352A1 for ; Tue, 6 Dec 2022 20:43:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229612AbiLFUns (ORCPT ); Tue, 6 Dec 2022 15:43:48 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37682 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229511AbiLFUnr (ORCPT ); Tue, 6 Dec 2022 15:43:47 -0500 Received: from sin.source.kernel.org (sin.source.kernel.org [IPv6:2604:1380:40e1:4800::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1BE3443851; Tue, 6 Dec 2022 12:43:47 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by sin.source.kernel.org (Postfix) with ESMTPS id 62FB9CE1ADE; Tue, 6 Dec 2022 20:43:45 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 50695C433D6; Tue, 6 Dec 2022 20:43:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1670359423; bh=nakWPfl/JPzwhzckIxUS+kQsv0RDMmrnqYA8gUFyCTU=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=BuO9tr0vZz7M2wK6L/5GF4fw5fBLo6XuXDKMiR57OmTVRZBjcVnBZBvbSuEJyHHsB yGqilZlLOvnL+mutjQ+vcsHgY3nMHcYGjYAMJZkSERm1BhaAXos5cZkR01zcjYJyMg EvsWl02E/vMK6KYMP47pa/HxNNkX23SzewQZ1lS65voS6xP8XIZCUns+4i5XXhEqj8 TKqXTwrtFLpU/YyDMAcY+tBtG8Cfvu0qXgsX6QjUjD/nkN4dijI0k2VisJVZNb9DuQ JXtaC97t0YjNy0mhNceK1zC6DhNvkTCgkGElSyAYXl4VFjdjOADHzUNY7RUYJdg8zJ ga7VKJM0FBLYQ== Date: Tue, 6 Dec 2022 12:43:42 -0800 From: Jakub Kicinski To: Justin Iurman Cc: Eric Dumazet , netdev@vger.kernel.org, davem@davemloft.net, yoshfuji@linux-ipv6.org, dsahern@kernel.org, pabeni@redhat.com, stable@vger.kernel.org Subject: Re: [RFC net] Fixes: b63c5478e9cb ("ipv6: ioam: Support for Queue depth data field") Message-ID: <20221206124342.7f429399@kernel.org> In-Reply-To: References: <20221205153557.28549-1-justin.iurman@uliege.be> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Mon, 5 Dec 2022 21:44:09 +0100 Justin Iurman wrote: > > Please revert this patch. > > > > Many people use FQ qdisc, where packets are waiting for their Earliest > > Departure Time to be released. > > The IOAM queue depth is a very important value and is already used. Can you say more about the use? What signal do you derive from it? I do track qlen on Meta's servers but haven't found a strong use for it yet (I did for backlog drops but not the qlen itself). > > Also, the draft says: > > > > 5.4.2.7. queue depth > > > > The "queue depth" field is a 4-octet unsigned integer field. This > > field indicates the current length of the egress interface queue of > > the interface from where the packet is forwarded out. The queue > > depth is expressed as the current amount of memory buffers used by > > the queue (a packet could consume one or more memory buffers, > > depending on its size). > > > > 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 > > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ > > | queue depth | > > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ > > > > > > It is relatively clear that the egress interface is the aggregate > > egress interface, > > not a subset of the interface. > > Correct, even though the definition of an interface in RFC 9197 is quite > abstract (see the end of section 4.4.2.2: "[...] could represent a > physical interface, a virtual or logical interface, or even a queue"). > > > If you have 32 TX queues on a NIC, all of them being backlogged (line rate), > > sensing the queue length of one of the queues would give a 97% error > > on the measure. > > Why would it? Not sure I get your idea based on that example. Because it measures the length of a single queue not the device.