Re: [Codel] fq_codel : interval servo

[Jim Gettys <jg@freedesktop.org>]

On 08/31/2012 10:31 AM, Rick Jones wrote:
> On 08/31/2012 10:15 AM, Jim Gettys wrote:
>> What is more, consumer ethernet switches do do flow control, whether you
>> want them to or not.
>
> My understanding is that Ethernet flow control (what ever its
> 802.1mumble might be?) is negotiated when the link is brought-up, and
> that both sides must agree before it will be active.  So, if you (the
> end station) do not want flow control, you can simply not accept it
> during link-up.
>
> Under Linux, the ethtool utility can be used to affect the
> configuration of "pause" (the name coming from the name of the frames
> used by flow control - "pause frames" if I recall correctly)

The cheap consumer switches typically have it on; and by default, most
ethernet drivers have it on by default.

That's how/why I found out about pause frames in the first place; I
wasn't looking for it, and the existence of these frames in wireshark
was a surprise to me.

This can cause "interesting" performance problems most consumers won't
understand when switches are layered.

Most enterprise switches will often have it off by default, or plain
never generate flow control frames at all.


                        - Jim