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=-3.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED autolearn=no 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 ABA76C433B4 for ; Mon, 17 May 2021 23:00:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8802761209 for ; Mon, 17 May 2021 23:00:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344342AbhEQXCG (ORCPT ); Mon, 17 May 2021 19:02:06 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43408 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238778AbhEQXCC (ORCPT ); Mon, 17 May 2021 19:02:02 -0400 Received: from mail-pl1-x630.google.com (mail-pl1-x630.google.com [IPv6:2607:f8b0:4864:20::630]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 76512C061756 for ; Mon, 17 May 2021 16:00:45 -0700 (PDT) Received: by mail-pl1-x630.google.com with SMTP id v13so3994342ple.9 for ; Mon, 17 May 2021 16:00:45 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=networkplumber-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:subject:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=J5UPtJBA2/uZss4lqlO0e1yXDcg7qUB+Zl/PUuJbbYE=; b=IWyM9sjVdu++omxyx1AMtdPQs4a0ozm7svxwu99rUMs1VRGo4TonL0IHdGzZb3uW5E xcXAAoCzpkvavTrGVB2nYvnsrfhEpqCrRXKN/hHngWLIfpgwnhEuoLK113dG/+BIyDuh Sj6y3fZ+nJNL/E6Q+hRNLJsBNkgTa4IqDF58R8kALne80FnSnzqfRr6HB5bVXC0tkqeQ 3kxCS7V/DJGPsrLZs4VpsAFy5CYCCtEcff8VQy/Mh/EjPJFrJ/hrYQgn8pgHqyZSwFBV zs9wSfEPs0gcw3SoFy5hNxoxojXZMLp32MFdnQMLB+8jHTDwfh5nlsImKnHT0O5aqk1g Eo/Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=J5UPtJBA2/uZss4lqlO0e1yXDcg7qUB+Zl/PUuJbbYE=; b=TzJ8NQ1+vrI8TafTqvodFpbq3qfoWKLs1mb/Miq3FchEPtTj761FgJ8uf7diL/ANuK 7W4RmI/yfdx+wfcyGgsT+qoyq5ruZuiTUjMoxyMb3vDRSZFIMyJCgA8mrx0APnI2nBKc HzYH4xbqQ3zvogGd7dsrdvK7S74Dd36hc1mAlNrsgRz2Ok+BhFSkJ/0qeShFn1AXF1jz +2u7E0IR82aU51Ij0k/8QBwDaYGjcj/zqb9QIJRnXfv68agqvuCEHeBuERbXIRyeEOYL Rs/hTZUtMeSHo784M7ie9uQG3WaP3HMtCgpvfs6cFsHZeEAHLG6NdeIS9wZJs/Pk3ANu IMDA== X-Gm-Message-State: AOAM532jxy5Usli0JUQwE1FIU/hnJxIgjyIGHrbk34cAYg7vtvhatGEp IfQ/GgYtkLpXLZ0yhL2qzI0Z6MGlmRkaKw== X-Google-Smtp-Source: ABdhPJzHx/GzyV+cs+RXbfCjINrLXRVbUF9R3U+E1uvDqWvR1mQ7fgDj9nswene7Drh2+s6SOT/zVA== X-Received: by 2002:a17:90a:aa96:: with SMTP id l22mr1517678pjq.173.1621292444994; Mon, 17 May 2021 16:00:44 -0700 (PDT) Received: from hermes.local (76-14-218-44.or.wavecable.com. [76.14.218.44]) by smtp.gmail.com with ESMTPSA id r5sm374912pjd.2.2021.05.17.16.00.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 17 May 2021 16:00:44 -0700 (PDT) Date: Mon, 17 May 2021 16:00:36 -0700 From: Stephen Hemminger To: Dave Taht Cc: Willem de Bruijn , "Michael S. Tsirkin" , Xianting Tian , Linux Kernel Network Developers , LKML , virtualization , bloat , Jakub Kicinski , "David S. Miller" Subject: Re: [Bloat] virtio_net: BQL? Message-ID: <20210517160036.4093d3f2@hermes.local> In-Reply-To: References: <56270996-33a6-d71b-d935-452dad121df7@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 17 May 2021 14:48:46 -0700 Dave Taht wrote: > On Mon, May 17, 2021 at 1:23 PM Willem de Bruijn > wrote: > > > > On Mon, May 17, 2021 at 2:44 PM Dave Taht wrote: > > > > > > Not really related to this patch, but is there some reason why virtio > > > has no support for BQL? > > > > There have been a few attempts to add it over the years. > > > > Most recently, https://lore.kernel.org/lkml/20181205225323.12555-2-mst@redhat.com/ > > > > That thread has a long discussion. I think the key open issue remains > > > > "The tricky part is the mode switching between napi and no napi." > > Oy, vey. > > I didn't pay any attention to that discussion, sadly enough. > > It's been about that long (2018) since I paid any attention to > bufferbloat in the cloud and my cloudy provider (linode) switched to > using virtio when I wasn't looking. For over a year now, I'd been > getting reports saying that comcast's pie rollout wasn't working as > well as expected, that evenroute's implementation of sch_cake and sqm > on inbound wasn't working right, nor pf_sense's and numerous other > issues at Internet scale. > > Last week I ran a string of benchmarks against starlink's new services > and was really aghast at what I found there, too. but the problem > seemed deeper than in just the dishy... > > Without BQL, there's no backpressure for fq_codel to do its thing. > None. My measurement servers aren't FQ-codeling > no matter how much load I put on them. Since that qdisc is the default > now in most linux distributions, I imagine that the bulk of the cloud > is now behaving as erratically as linux was in 2011 with enormous > swings in throughput and latency from GSO/TSO hitting overlarge rx/tx > rings, [1], breaking various rate estimators in codel, pie and the tcp > stack itself. > > See: > > http://fremont.starlink.taht.net/~d/virtio_nobql/rrul_-_evenroute_v3_server_fq_codel.png > > See the swings in latency there? that's symptomatic of tx/rx rings > filling and emptying. > > it wasn't until I switched my measurement server temporarily over to > sch_fq that I got a rrul result that was close to the results we used > to get from the virtualized e1000e drivers we were using in 2014. > > http://fremont.starlink.taht.net/~d/virtio_nobql/rrul_-_evenroute_v3_server_fq.png > > While I have long supported the use of sch_fq for tcp-heavy workloads, > it still behaves better with bql in place, and fq_codel is better for > generic workloads... but needs bql based backpressure to kick in. > > [1] I really hope I'm overreacting but, um, er, could someone(s) spin > up a new patch that does bql in some way even half right for this > driver and help test it? I haven't built a kernel in a while. > The Azure network driver (netvsc) also does not have BQL. Several years ago I tried adding it but it benchmarked worse and there is the added complexity of handling the accelerated networking VF path.