On Mon, May 17, 2021 at 4:00 PM Stephen Hemminger <[email protected]> wrote: > > On Mon, 17 May 2021 14:48:46 -0700 > Dave Taht <[email protected]> wrote: > > > On Mon, May 17, 2021 at 1:23 PM Willem de Bruijn > > <[email protected]> wrote: > > > > > > On Mon, May 17, 2021 at 2:44 PM Dave Taht <[email protected]> wrote: > > > > > > > > Not really related to this patch, but is there some reason why virtio > > > > has no support for BQL? > > > > > > There have been a few attempts to add it over the years. > > > > > > Most recently, > > > https://lore.kernel.org/lkml/[email protected]/ > > > > > > That thread has a long discussion. I think the key open issue remains > > > > > > "The tricky part is the mode switching between napi and no napi." > > > > Oy, vey. > > > > I didn't pay any attention to that discussion, sadly enough. > > > > It's been about that long (2018) since I paid any attention to > > bufferbloat in the cloud and my cloudy provider (linode) switched to > > using virtio when I wasn't looking. For over a year now, I'd been > > getting reports saying that comcast's pie rollout wasn't working as > > well as expected, that evenroute's implementation of sch_cake and sqm > > on inbound wasn't working right, nor pf_sense's and numerous other > > issues at Internet scale. > > > > Last week I ran a string of benchmarks against starlink's new services > > and was really aghast at what I found there, too. but the problem > > seemed deeper than in just the dishy... > > > > Without BQL, there's no backpressure for fq_codel to do its thing. > > None. My measurement servers aren't FQ-codeling > > no matter how much load I put on them. Since that qdisc is the default > > now in most linux distributions, I imagine that the bulk of the cloud > > is now behaving as erratically as linux was in 2011 with enormous > > swings in throughput and latency from GSO/TSO hitting overlarge rx/tx > > rings, [1], breaking various rate estimators in codel, pie and the tcp > > stack itself. > > > > See: > > > > http://fremont.starlink.taht.net/~d/virtio_nobql/rrul_-_evenroute_v3_server_fq_codel.png > > > > See the swings in latency there? that's symptomatic of tx/rx rings > > filling and emptying. > > > > it wasn't until I switched my measurement server temporarily over to > > sch_fq that I got a rrul result that was close to the results we used > > to get from the virtualized e1000e drivers we were using in 2014. > > > > http://fremont.starlink.taht.net/~d/virtio_nobql/rrul_-_evenroute_v3_server_fq.png > > > > While I have long supported the use of sch_fq for tcp-heavy workloads, > > it still behaves better with bql in place, and fq_codel is better for > > generic workloads... but needs bql based backpressure to kick in. > > > > [1] I really hope I'm overreacting but, um, er, could someone(s) spin > > up a new patch that does bql in some way even half right for this > > driver and help test it? I haven't built a kernel in a while. > > > > The Azure network driver (netvsc) also does not have BQL. Several years ago > I tried adding it but it benchmarked worse and there is the added complexity > of handling the accelerated networking VF path.
I certainly agree it adds complexity, but the question is what sort of network behavior resulted without backpressure inside the vm? What sorts of benchmarks did you do? I will get setup to do some testing of this that is less adhoc. -- Latest Podcast: https://www.linkedin.com/feed/update/urn:li:activity:6791014284936785920/ Dave Täht CTO, TekLibre, LLC _______________________________________________ Bloat mailing list [email protected] https://lists.bufferbloat.net/listinfo/bloat
