netdev - Re: BBR and TCP internal pacing causing interrupt storm with pfifo

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Date:   Mon, 15 Oct 2018 12:26:06 +0200
From:   Gasper Zejn <zelo.zejn@...il.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     Eric Dumazet <eric.dumazet@...il.com>, Kevin Yang <yyd@...gle.com>,
        netdev <netdev@...r.kernel.org>
Subject: Re: BBR and TCP internal pacing causing interrupt storm with
 pfifo_fast


On 09. 10. 2018 19:26, Eric Dumazet wrote:
> On Tue, Oct 9, 2018 at 10:22 AM Gasper Zejn <zelo.zejn@...il.com> wrote:
>> On 09. 10. 2018 19:00, Eric Dumazet wrote:
>>> On 10/09/2018 09:38 AM, Gasper Zejn wrote:
>>>> Hello,
>>>>
>>>> I am seeing interrupt storms of over 100k-900k local timer interrupts
>>>> when changing between network devices or networks with open TCP
>>>> connections when not using sch_fq (I was using pfifo_fast). Using sch_fq
>>>> makes the bug with interrupt storm go away.
>>>>
>>> That is for what kind of traffic ?
>>>
>>> If your TCP flows send 100k-3M packets per second, then yes, the pacing timers
>>> could be setup in the 100k-900k range.
>>>
>> Traffic is nowhere in that range, think of having a few browser tabs of
>> javascript rich
>> web pages open, mostly idle, for example slack, gmail or tweetdeck. No
>> significant
>> packet rate is needed, just open connections.
> No idea of what is going on really. A repro would be nice.

I've tried to isolate the issue as best I could. There seems to be an
issue if the TCP socket has keepalive set and send queue is not empty
and the route goes away.

https://github.com/zejn/bbr_pfifo_interrupts_issue

Hope this helps,
Gasper