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From: Neal Cardwell <ncardwell@google.com>
To: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: erik.taraldsen@telenor.com,
	Priyaranjan Jha <priyarjha@google.com>,
	 bloat <bloat@lists.bufferbloat.net>
Subject: Re: [Bloat] BBR implementations, knobs to turn?
Date: Fri, 20 Nov 2020 18:34:04 -0500	[thread overview]
Message-ID: <CADVnQy=ENdj8J+o9K4z4zODCGYDb+e110GpGs8N+Z=PcrkMr4Q@mail.gmail.com> (raw)
In-Reply-To: <20201117160744.395f108e@carbon>

On Tue, Nov 17, 2020 at 10:08 AM Jesper Dangaard Brouer
<brouer@redhat.com> wrote:
>
> On Tue, 17 Nov 2020 10:05:24 +0000 <erik.taraldsen@telenor.com> wrote:
>
> > Thank you for the response Neal
>
> Yes. And it is impressive how many highly qualified people are on the
> bufferbloat list.
>
> > old_hw # uname -r
> > 5.3.0-64-generic
> > (Ubuntu 19.10 on xenon workstation, integrated network card, 1Gbit
> > GPON access.  Used as proof of concept from the lab at work)
> >
> >
> > new_hw # uname -r
> > 4.18.0-193.19.1.el8_2.x86_64
> > (Centos 8.2 on xenon rack server, discrete 10Gbit network card,
> > 40Gbit server farm link (low utilization on link), intended as fully
> > supported and run service.  Not possible to have newer kernel and
> > still get service agreement in my organization)
>
> Let me help out here.  The CentOS/RHEL8 kernels have a huge amount of
> backports.  I've attached a patch/diff of net/ipv4/tcp_bbr.c changes
> missing in RHEL8.
>
> It looks like these patches are missing in CentOS/RHEL8:
>  [1] https://git.kernel.org/torvalds/c/78dc70ebaa38aa3
>  [2] https://git.kernel.org/torvalds/c/a87c83d5ee25cf7
>
> Could missing patch [1] result in the issue Erik is seeing?
> (It explicitly mentions improvements for WiFi...)

Thanks, Erik, for the detailed information. This is super-useful.

And thanks, Jesper, for the patch analysis. Yes, I agree that missing
patch [1]  is likely the cause of the lower BBR throughout in the
"new_hw" case. Since the "new_hw" is running an older kernel that's
missing this important patch, it would be expected to have lower
throughput in a workload like this. It's unfortunate that it's not
possible to have a newer kernel on the newer hardware; it does seem in
this case that this would probably do the trick.

best,
neal

      parent reply	other threads:[~2020-11-20 23:34 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-16 15:25 erik.taraldsen
2020-11-16 21:14 ` Neal Cardwell
2020-11-17 10:05   ` erik.taraldsen
2020-11-17 15:07     ` Jesper Dangaard Brouer
2020-11-19  7:57       ` erik.taraldsen
2020-11-19 13:32         ` Luca Muscariello
2020-11-19 14:35           ` erik.taraldsen
2020-11-20 11:10             ` Jesper Dangaard Brouer
2020-11-20 12:42               ` Toke Høiland-Jørgensen
2020-11-23 12:57                 ` erik.taraldsen
2020-11-30 17:18                   ` Aaron Wood
2020-11-20 23:34       ` Neal Cardwell [this message]

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