From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-il1-x130.google.com (mail-il1-x130.google.com [IPv6:2607:f8b0:4864:20::130]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.bufferbloat.net (Postfix) with ESMTPS id 116523B29E for ; Mon, 17 May 2021 17:48:59 -0400 (EDT) Received: by mail-il1-x130.google.com with SMTP id k4so3661424ili.4 for ; Mon, 17 May 2021 14:48:59 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc:content-transfer-encoding; bh=5k+CB7+a281FNvx4AyiO3QnFARm73PakcEl2o60CjU0=; b=Byg+eK9Ri8MLuHrFeOzSlMEqt8c+nOthtNHB2zWpR2gdR9+jDhnbv3eQz6Bz3e6KfT O5nmBP3lCxBqBCGs5iKzyQIwF9mttkHstrRTusVt0o3r/NqTGJY7jcyRsV3MfKutz8sz Dz+j9p0UPByLCL+3nS99hkh5KufrlEbig5C94K1F45f7w6fiUNaaFhGdo62My7Y8jdaC 7dt4Koiu0YT60GRN56mnhv/OuVl2SqRaua3+OWPvjhFQnaJ7+56Dv2KvfxpL+YiRtoAT nmNIK6EzoWNt1bjwmhuis+pSZ24mJKrFiKKVU0UcQJ78nZZAoHVpt5OhUfLeGTFds6sm KBPw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc:content-transfer-encoding; bh=5k+CB7+a281FNvx4AyiO3QnFARm73PakcEl2o60CjU0=; b=Ajkw0+TErkXuCskS05/w/WHrHi31W6y2bsT3VVgzv+eG7itC4KyoyLsN3Ck17UlNQL kvcqSLq5ocKIL8jr4Jx2u4dqm+Gvsq/AwrFuyHK2aRTIY/TxbsGCxaAnrtrJkC1hQPJq 9a7oIFv7MGDHN9bLLtFkAf5VtGTaCyiFKMQNR39fWB5u+6kBGvsUnymuIFB9GCfqpYE8 n73xGv8gPbhzXzWJv1LEKQaLPFiu6nLR3OwRkzq3aC3QdMwSgyoHVyChTywMvhqSWpdz 47eauQKzG+JZjafl4vZRKJw57yZ39F79IkGlMaUHUIzRJoV1oM97Y5802Jyw2r8k/PKJ PVdw== X-Gm-Message-State: AOAM533VOX56HSs/zq9VpRLRSusuDu+QJir576EOPUfZAlenwxO4f37u ALVCTFEhLWYyrLCh7Wk7dre3eqATj/gm+t3+kiY= X-Google-Smtp-Source: ABdhPJwXdm3VL7bieUMtr1BfTjcSmohISUpITGC6QuDiCZ7r6aZrLr+fVUI/Vhh97A0izC4hduG3W7JYPpTz6MfQ1ZI= X-Received: by 2002:a05:6e02:1ba5:: with SMTP id n5mr1392214ili.45.1621288139279; Mon, 17 May 2021 14:48:59 -0700 (PDT) MIME-Version: 1.0 References: <56270996-33a6-d71b-d935-452dad121df7@linux.alibaba.com> In-Reply-To: From: Dave Taht Date: Mon, 17 May 2021 14:48:46 -0700 Message-ID: To: Willem de Bruijn Cc: Xianting Tian , "Michael S. Tsirkin" , Jason Wang , "David S. Miller" , Jakub Kicinski , virtualization , Linux Kernel Network Developers , LKML , bloat Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Subject: Re: [Bloat] virtio_net: BQL? X-BeenThere: bloat@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: General list for discussing Bufferbloat List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 17 May 2021 21:49:00 -0000 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@re= dhat.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. > > On Mon, May 17, 2021 at 11:41 AM Xianting Tian > > wrote: > > > > > > BUG_ON() uses unlikely in if(), which can be optimized at compile tim= e. > > > > > > Signed-off-by: Xianting Tian > > > --- > > > drivers/net/virtio_net.c | 5 ++--- > > > 1 file changed, 2 insertions(+), 3 deletions(-) > > > > > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > > > index c921ebf3ae82..212d52204884 100644 > > > --- a/drivers/net/virtio_net.c > > > +++ b/drivers/net/virtio_net.c > > > @@ -1646,10 +1646,9 @@ static int xmit_skb(struct send_queue *sq, str= uct > > > sk_buff *skb) > > > else > > > hdr =3D skb_vnet_hdr(skb); > > > > > > - if (virtio_net_hdr_from_skb(skb, &hdr->hdr, > > > + BUG_ON(virtio_net_hdr_from_skb(skb, &hdr->hdr, > > > virtio_is_little_endian(vi->vdev)= , false, > > > - 0)) > > > - BUG(); > > > + 0)); > > > > > > if (vi->mergeable_rx_bufs) > > > hdr->num_buffers =3D 0; > > > -- > > > 2.17.1 > > > > > > > > > -- > > Latest Podcast: > > https://www.linkedin.com/feed/update/urn:li:activity:679101428493678592= 0/ > > > > Dave T=C3=A4ht CTO, TekLibre, LLC -- Latest Podcast: https://www.linkedin.com/feed/update/urn:li:activity:6791014284936785920/ Dave T=C3=A4ht CTO, TekLibre, LLC