On Mon, May 17, 2021 at 1:23 PM Willem de Bruijn <willemdebruijn.ker...@gmail.com> wrote: > > On Mon, May 17, 2021 at 2:44 PM Dave Taht <dave.t...@gmail.com> 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/20181205225323.12555-2-...@redhat.com/ > > 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. > > On Mon, May 17, 2021 at 11:41 AM Xianting Tian > > <xianting.t...@linux.alibaba.com> wrote: > > > > > > BUG_ON() uses unlikely in if(), which can be optimized at compile time. > > > > > > Signed-off-by: Xianting Tian <xianting.t...@linux.alibaba.com> > > > --- > > > drivers/net/virtio_net.c | 5 ++--- > > > 1 file changed, 2 insertions(+), 3 deletions(-) > > > > > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > > > index c921ebf3ae82..212d52204884 100644 > > > --- a/drivers/net/virtio_net.c > > > +++ b/drivers/net/virtio_net.c > > > @@ -1646,10 +1646,9 @@ static int xmit_skb(struct send_queue *sq, struct > > > sk_buff *skb) > > > else > > > hdr = skb_vnet_hdr(skb); > > > > > > - if (virtio_net_hdr_from_skb(skb, &hdr->hdr, > > > + BUG_ON(virtio_net_hdr_from_skb(skb, &hdr->hdr, > > > virtio_is_little_endian(vi->vdev), > > > false, > > > - 0)) > > > - BUG(); > > > + 0)); > > > > > > if (vi->mergeable_rx_bufs) > > > hdr->num_buffers = 0; > > > -- > > > 2.17.1 > > > > > > > > > -- > > Latest Podcast: > > https://www.linkedin.com/feed/update/urn:li:activity:6791014284936785920/ > > > > Dave Täht CTO, TekLibre, LLC -- Latest Podcast: https://www.linkedin.com/feed/update/urn:li:activity:6791014284936785920/ Dave Täht CTO, TekLibre, LLC _______________________________________________ Bloat mailing list Bloat@lists.bufferbloat.net https://lists.bufferbloat.net/listinfo/bloat