On Wed, 29 May 2013 16:18:26 -0700 Eric Dumazet <[email protected]> wrote: > On Wed, 2013-05-29 at 15:50 -0700, Stephen Hemminger wrote: > > On Wed, 29 May 2013 08:52:04 -0700 > > Eric Dumazet <[email protected]> wrote: > > > > > On Wed, 2013-05-29 at 15:13 +0200, Jesper Dangaard Brouer wrote: > > > > I recently discovered that the (traffic control) tc linklayer > > > > calculations for ATM/ADSL have been broken by: > > > > commit 56b765b79 (htb: improved accuracy at high rates). > > > > > > > > Thus, people shaping on ADSL links, using e.g.: > > > > tc class add ... htb rate X ceil Y linklayer atm overhead 10 > > > > > > > > Will no-longer get ATM cell tax/overhead adjusted. > > > > > > Adding the logic on the kernel is doable, by adding some clean > attributes so that tc can setup the feature, and report the attributes > back.
Yes, doing the logic in the kernel might be a better solution. But the question is how do we keep iproute2 backward compatible with older kernels? > cpus are fast today and can perform the atm cell/overhead faster than > a table lookup. Do remember that the target CPU is small embedded router boxes. BUT I do agree that, the following code required, is probably faster than a table lookup: int pkt_len = skb->len + (encap_overhead * gso_segments); int wire_sz = DIV_ROUND_UP(pkt_len,48)*53; (I suspect, that the compiler might even optimize and remove any real divisions, I bet Eric can tell us.) Looking at how simple the above code is, I'm a little appalled by all the table lookup infrastructure and hacks we added, to support/implement this. -- Best regards, Jesper Dangaard Brouer MSc.CS, Sr. Network Kernel Developer at Red Hat Author of http://www.iptv-analyzer.org LinkedIn: http://www.linkedin.com/in/brouer _______________________________________________ Bloat mailing list [email protected] https://lists.bufferbloat.net/listinfo/bloat
