Re: [Cake] [PATCH net-next v7 6/7] sch_cake: Add overhead compensation support to the rate shaper

[Sebastian Moeller <moeller0@gmx.de>]

> On May 2, 2018, at 17:11, Toke Høiland-Jørgensen <toke@toke.dk> wrote:
> 
> +		/* The last segment may be shorter; we ignore this, which means
> +		 * that we will over-estimate the size of the whole GSO segment
> +		 * by the difference in size. This is conservative, so we live
> +		 * with that to avoid the complexity of dealing with it.
> +		 */
> +		len = shinfo->gso_size + hdr_len;
> +	}


Hi Toke,

so I am on the fence with this one, as the extreme case is having a super packet consisting out of 1 full-MTU packet plus a tiny leftover in that case we pay a 50% bandwidth sacrifice which seems a bit high. Nowm I have no real feling how likely this full MTU plus 64 byte packet issue is in real life, but in the past I often saw maximum packetsizes of around 3K bytes on my router indicating that having a sup packet consisting just out of two segments might not be that rare. So is there an easy way for me to measure the probability of seeing that issue?
I am all for sacrificing some bandwidth for better latency under load, but few users will be happy with a 50% loss of bandwidth...

Best Regards
	Sebastian