Note: I am at nanog this week, expect replies to be sparse to non-existent. On Mon, Jun 1, 2015 at 12:17 PM, Robert LeBlanc <robert@xxxxxxxxxxxxx> wrote: > I wondered about the queue depth of sfq as well. I changed out the > prio and sfq to fq_codel. The problem persisted, although it looks > like we found another issue. I am not a believer in strict prio queuing, preferring weighted DRR if you must have classes of traffic. > Performance on the target host just tanked and never recovered. We > found ksoftirqd eating tons of CPU time. > From what I understand > (please help my understanding if I'm wrong) the kernel stopped > handling interrupts in hardware and started handling them all in the > kernel dropping performance. A reboot of the host restored performance > and lowered ksoftirqd utilization although it is still no where the 40 ksoftirqd is used for many things. Were you also attempting to use htb to rate limit? Don't do that. Try something that has no inherent rate limits if you must do more prioritization - but look over sch_fq's features carefully, it probably does what you want. > Gb of line rate of the adapter or even a quarter that. I think the > i40e driver still has a way to go before good performance can be > expected. Latest kernels had quite a few optimizations for 40GigE, notably BQL bulking and FIB table improvements. Prior to the BQL bulk changes 40GigE was unachievable. > I was looking for some good info on sch_fq last week, but couldn't > find anything. Do you have links? It has become recently apparent that better documentation and discussion of sch_fq is needed. I am not the author (nor am I of fq_codel!) and my own focus is primarily on fixing the edge networks, particularly wifi these days, and as huge a fan as I am of sch_fq and pacing, it's (very strong!) applicability in the data center is where I do not venture personally. I strongly encourage experimentation and good measurements on your own workloads, and publishing your scripts and results. :) Give it a shot. > > Thanks, > ---------------- > Robert LeBlanc > GPG Fingerprint 79A2 9CA4 6CC4 45DD A904 C70E E654 3BB2 FA62 B9F1 > > > On Mon, Jun 1, 2015 at 12:12 PM, Dave Taht <dave.taht@xxxxxxxxx> wrote: >> On Mon, Jun 1, 2015 at 10:06 AM, jsullivan@xxxxxxxxxxxxxxxxxxx >> <jsullivan@xxxxxxxxxxxxxxxxxxx> wrote: >>> >>>> On June 1, 2015 at 12:36 PM Andy Furniss <adf.lists@xxxxxxxxx> wrote: >>>> >>>> >>>> Robert LeBlanc wrote: >>>> > -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 >>>> > >>>> > Any ideas on this? >>>> >>>> 40 gig nics are way beyond anything I've ever done with tc and I guess >>>> involve some offload = huge "packets". >>>> >>>> It could be that aas sfq has a default qlen of 128 and as you are not >>>> actually rate limiting (and to do that may be "interesting" at 80 gig) >>>> the prio relies on some downstream buffer being full. Perhaps it's just >>>> that at these rates prio can not dequeue anything for periods of time so >>>> the 128 limit of sfq is overrun even for the highest prio. >>>> >>>> This is pure guesswork. >>>> -- >>>> 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 >>> >>> Alas, I haven't yet read the details of the original post but I know we just >>> replaced all our sfq leaves with fq_codel because of concerns about the per flow >>> packet depth on high speed, high latency networks. >> >> Yes, older versions of SFQ had a hard limit on queue depth. This was >> "improved" in linux 3.6 and later but that work ultimately pointed at >> a need to actively manage the queue depth, which begat sfqred, and >> ultimately fq_codel. >> >> I note that, these days, the best results we get for >> tcp-heavy-*servers and hosts* (not routers, not udp heavy services, >> and the bare metal under a vm is a "router" in this context), in the >> data center, at these speeds, now come from sch_fq (from the pacing, >> fq, and tso fixes), and a low setting for tcp_limit_output_bytes. >> >> example: >> >> https://fasterdata.es.net/host-tuning/linux/fair-queuing-scheduler/ >> >> fq_codel remains a great all-around choice, but what pacing is doing >> is really remarkable for servers in sch_fq. >> >>> -- >>> 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 >> >> >> >> -- >> Dave Täht >> What will it take to vastly improve wifi for everyone? >> https://plus.google.com/u/0/explore/makewififast -- Dave Täht What will it take to vastly improve wifi for everyone? https://plus.google.com/u/0/explore/makewififast -- 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
