Sebastian Moeller wrote:
Thanks for sharing your test case; I can repeat these results exactly on my machines (I also tried htb instead hfsc for fun: same result as to be expected see below). Looking back at http://lxr.free-electrons.com/ident?i=qdisc_pkt_len_init (line 2731): qdisc_skb_cb(skb)->pkt_len += (gso_segs - 1) * hdr_len ; I begin to realize this function is not responsible for adding single wire packet’s ethernet header, but for figuring out in how many on-the-wire packets to chop down a GSO packet , and add the header overhead for the additional wire packets, I had completely looked over the (gso-segs - 1) part, oops.
Glad it helped - I know from trying, and giving up, how hard/error prone reading kernel code can be :-)
@cerowrt-devel: everyone using link layer ATM you might want to try to reduce the the per packet overhead by 14… (but please test)
Maybe you mean overhead calculated by a script? Just to be clear, I expect that wrt would be shaping on ppp, so you don't need to take 14 if that's the case.
So I stand corrected, you are right, tic’s stab automatically adds the ethernet header. So I am off to repeat my netperf-wrapper tests right now again with overhead of 30 instead of 44, again these tests confirm your observation. Interestingly, it seems netperf-wrapper’s RRUL test really is suited to figure out the overhead: while shaping to 100% of line rate (on ADSL2+ where line rate rate is the net line rate (after FEC)) specifying too small an overhead the ICMP latency plot shows larger deviations from the expected unload RTT plus 10ms. Too large an overhead however just decreases the good put bait while leaving the latency well under control.
I wouldn't word it like "stab adds ..." This is nothing to do with stab really - just the only length stab knows is skb->len and that means different things on different interfaces because of how the kernel works. (I haven't retested all this, but I doubt it's changed) On ppp skb->len = ip len On eth skb->len = ip len + 14 On vlan skb->len = ip len + 18 If you ran my script on various interfaces without stab I expect you would still be able to see the difference - everyone who does any tc on eth gets shaping with ip+14 sized packets. Even without tc involved I think you could see the difference looking at ip -s ls xxxx type stats on different interfaces. -- To unsubscribe from this list: send the line "unsubscribe lartc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
