What queues/buffers does tc-netem use?

What queues/buffers does tc-netem use?

[Motejlek, Petr]

Hello,

I was wondering what queues/buffers does netem use and how does one control or monitor them?

I could not find this information anywhere and I am not that good in reading the sources to be able to tell enough about this :) If we talk only about the situation where netem is the root qdisc for a particular interface, I would imagine it might be using the txqueue of that interface, but I am not sure if that's really the case...

Thanks​,
Petr MOTEJLEK

Re: What queues/buffers does tc-netem use?

[Hagen Paul Pfeifer]

> On July 16, 2015 at 1:28 PM "Motejlek, Petr" <pmotejle@akamai.com>
> wrote:

> I was wondering what queues/buffers does netem use and how does one
> control or monitor them?

netem uses his own rbtree based queue. You can use tc(1) to get
statistics.

> I could not find this information anywhere and I am not that good in
> reading the sources to be able to tell enough about this :) If we talk
> only about the situation where netem is the root qdisc for a particular
> interface, I would imagine it might be using the txqueue of that
> interface, but I am not sure if that's really the case...

Saddly there is no netem implementation documentation, but the source code
is straightforward. You may take a look:

http://lxr.free-electrons.com/source/net/sched/sch_netem.c

Cheers, Hagen

Re: What queues/buffers does tc-netem use?

[Motejlek, Petr]

Hello Hagen,

Could you please give me some example of such a tc command that would tell me the statistics? I am not sure what you mean.

Is there a way I can manipulate the internal rbtree queue size, please?

Thank you

Petr MOTEJLEK
________________________________________
From: Hagen Paul Pfeifer <hagen@jauu.net>
Sent: Thursday, July 16, 2015 2:42 PM
To: netdev@vger.kernel.org; Motejlek, Petr
Cc: netem@osdl.org
Subject: Re: What queues/buffers does tc-netem use?

> On July 16, 2015 at 1:28 PM "Motejlek, Petr" <pmotejle@akamai.com>
> wrote:

> I was wondering what queues/buffers does netem use and how does one
> control or monitor them?

netem uses his own rbtree based queue. You can use tc(1) to get
statistics.

> I could not find this information anywhere and I am not that good in
> reading the sources to be able to tell enough about this :) If we talk
> only about the situation where netem is the root qdisc for a particular
> interface, I would imagine it might be using the txqueue of that
> interface, but I am not sure if that's really the case...

Saddly there is no netem implementation documentation, but the source code
is straightforward. You may take a look:

http://lxr.free-electrons.com/source/net/sched/sch_netem.c

Cheers, Hagen

Re: What queues/buffers does tc-netem use?

[Hagen Paul Pfeifer]

> On July 16, 2015 at 2:48 PM "Motejlek, Petr" <pmotejle@akamai.com>
> wrote:
>
> Could you please give me some example of such a tc command that
> would tell me the statistics? I am not sure what you mean.

tc -s qdisc show dev eth0

> Is there a way I can manipulate the internal rbtree queue size, please?

Sure, the option is called limit.
 
> Thank you

You are welcome!

Hagen