netdev - Re: tuntap: Overload handling

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Message-ID: <CAGUzgd+fVUEc6wqHbTdygAfbhuck5Hy7odtoGTFVQToHy6_7eg@mail.gmail.com>
Date:	Fri, 15 Feb 2013 08:04:44 +0100
From:	Sebastian Pöhn <sebastian.poehn@...glemail.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	"Michael S. Tsirkin" <mst@...hat.com>, netdev@...r.kernel.org
Subject: Re: tuntap: Overload handling

Ok, thanks. So if you think of tuntap as a virtual device (and that's
what it is) then the drop behavior is quite a valid way.

So I'll gonna try to use the "old" version with qdisc support and
extend it be the features I need.

On Thu, Feb 14, 2013 at 6:01 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Thu, 2013-02-14 at 18:42 +0200, Michael S. Tsirkin wrote:
>
>> Hmm so ~1000 packets in the tun queue is not enough?
>> You always have the option to increase it some more ...
>>
>> > You should ask Michael S. Tsirkin, as he removed the flow control
>> > in commit 5d097109257c03a71845729f8db6b5770c4bbedc
>> > (tun: only queue packets on device)
>> >
>>
>> Eric in the past you said the following things
>> (http://lkml.indiana.edu/hypermail/linux/kernel/1204.1/00784.html)
>> > > In your case I would just not use qdisc at all, like other virtual
>> > > devices.
>> ...
>> > > Anyway, with a 500 packet limit in TUN queue itself, qdisc layer should
>> > > be always empty. Whats the point storing more than 500 packets for a
>> > > device ? Thats a latency killer.
>> you don't think this applies, anymore?
>>
>
> Users have the choice to setup a qdisc or not.
>
> Having no qdisc can help raw performance, at the expense of bufferbloat.
> Thats all I was saying.
>
> It seems tun.c has no longer the possibility to effectively use a qdisc,
> (allowing the queue to buildup at qdisc layer)
>
>
>
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