On 6 May 2016 at 15:47, Jesper Dangaard Brouer <bro...@redhat.com> wrote: > > I've created a OpenWRT ticket[1] on this issue, as it seems that someone[2] > closed Felix'es OpenWRT email account (bad choice! emails bouncing). > Sounds like OpenWRT and the LEDE https://www.lede-project.org/ project > is in some kind of conflict. > > OpenWRT ticket [1] https://dev.openwrt.org/ticket/22349 > > [2] > http://thread.gmane.org/gmane.comp.embedded.openwrt.devel/40298/focus=40335
OK, so, after porting the patch to 4.1 openwrt kernel and playing a bit with fq_codel limits I was able to get 420Mbps UDP like this: tc qdisc replace dev wlan0 parent :1 fq_codel flows 16 limit 256 This is certainly better than 30Mbps but still more than two times less than before (900). TCP also improved a little (550 to ~590). Felix, others, do you want to see the ported patch, maybe I did something wrong? Doesn't look like it will save ath10k from performance regression. > > On Fri, 6 May 2016 11:42:43 +0200 > Jesper Dangaard Brouer <bro...@redhat.com> wrote: > >> Hi Felix, >> >> This is an important fix for OpenWRT, please read! >> >> OpenWRT changed the default fq_codel sch->limit from 10240 to 1024, >> without also adjusting q->flows_cnt. Eric explains below that you must >> also adjust the buckets (q->flows_cnt) for this not to break. (Just >> adjust it to 128) >> >> Problematic OpenWRT commit in question: >> http://git.openwrt.org/?p=openwrt.git;a=patch;h=12cd6578084e >> 12cd6578084e ("kernel: revert fq_codel quantum override to prevent it from >> causing too much cpu load with higher speed (#21326)") >> >> >> I also highly recommend you cherry-pick this very recent commit: >> net-next: 9d18562a2278 ("fq_codel: add batch ability to fq_codel_drop()") >> https://git.kernel.org/davem/net-next/c/9d18562a227 >> >> This should fix very high CPU usage in-case fq_codel goes into drop mode. >> The problem is that drop mode was considered rare, and implementation >> wise it was chosen to be more expensive (to save cycles on normal mode). >> Unfortunately is it easy to trigger with an UDP flood. Drop mode is >> especially expensive for smaller devices, as it scans a 4K big array, >> thus 64 cache misses for small devices! >> >> The fix is to allow drop-mode to bulk-drop more packets when entering >> drop-mode (default 64 bulk drop). That way we don't suddenly >> experience a significantly higher processing cost per packet, but >> instead can amortize this. >> >> To Eric, should we recommend OpenWRT to adjust default (max) 64 bulk >> drop, given we also recommend bucket size to be 128 ? (thus the amount >> of memory to scan is less, but their CPU is also much smaller). >> >> --Jesper >> >> >> On Thu, 05 May 2016 12:23:27 -0700 Eric Dumazet <eric.duma...@gmail.com> >> wrote: >> >> > On Thu, 2016-05-05 at 19:25 +0300, Roman Yeryomin wrote: >> > > On 5 May 2016 at 19:12, Eric Dumazet <eric.duma...@gmail.com> wrote: >> > > > On Thu, 2016-05-05 at 17:53 +0300, Roman Yeryomin wrote: >> > > > >> > > >> >> > > >> qdisc fq_codel 0: dev eth0 root refcnt 2 limit 1024p flows 1024 >> > > >> quantum 1514 target 5.0ms interval 100.0ms ecn >> > > >> Sent 12306 bytes 128 pkt (dropped 0, overlimits 0 requeues 0) >> > > >> backlog 0b 0p requeues 0 >> > > >> maxpacket 0 drop_overlimit 0 new_flow_count 0 ecn_mark 0 >> > > >> new_flows_len 0 old_flows_len 0 >> > > > >> > > > >> > > > Limit of 1024 packets and 1024 flows is not wise I think. >> > > > >> > > > (If all buckets are in use, each bucket has a virtual queue of 1 >> > > > packet, >> > > > which is almost the same than having no queue at all) >> > > > >> > > > I suggest to have at least 8 packets per bucket, to let Codel have a >> > > > chance to trigger. >> > > > >> > > > So you could either reduce number of buckets to 128 (if memory is >> > > > tight), or increase limit to 8192. >> > > >> > > Will try, but what I've posted is default, I didn't change/configure >> > > that. >> > >> > fq_codel has a default of 10240 packets and 1024 buckets. >> > >> > http://lxr.free-electrons.com/source/net/sched/sch_fq_codel.c#L413 >> > >> > If someone changed that in the linux variant you use, he probably should >> > explain the rationale. > > -- > Best regards, > Jesper Dangaard Brouer > MSc.CS, Principal Kernel Engineer at Red Hat > Author of http://www.iptv-analyzer.org > LinkedIn: http://www.linkedin.com/in/brouer _______________________________________________ openwrt-devel mailing list openwrt-devel@lists.openwrt.org https://lists.openwrt.org/cgi-bin/mailman/listinfo/openwrt-devel
