Re: [net-next v5 1/2] net: sched: use queue_mapping to pick tx queue

[Tonghao Zhang <xiangxia.m.yue@gmail.com>]

On Thu, Dec 30, 2021 at 3:14 AM Vinicius Costa Gomes
<vinicius.gomes@intel.com> wrote:
>
> xiangxia.m.yue@gmail.com writes:
>
> > From: Tonghao Zhang <xiangxia.m.yue@gmail.com>
> >
> > This patch fixes issue:
> > * If we install tc filters with act_skbedit in clsact hook.
> >   It doesn't work, because netdev_core_pick_tx() overwrites
> >   queue_mapping.
> >
> >   $ tc filter ... action skbedit queue_mapping 1
> >
> > And this patch is useful:
> > * We can use FQ + EDT to implement efficient policies. Tx queues
> >   are picked by xps, ndo_select_queue of netdev driver, or skb hash
> >   in netdev_core_pick_tx(). In fact, the netdev driver, and skb
> >   hash are _not_ under control. xps uses the CPUs map to select Tx
> >   queues, but we can't figure out which task_struct of pod/containter
> >   running on this cpu in most case. We can use clsact filters to classify
> >   one pod/container traffic to one Tx queue. Why ?
> >
> >   In containter networking environment, there are two kinds of pod/
> >   containter/net-namespace. One kind (e.g. P1, P2), the high throughput
> >   is key in these applications. But avoid running out of network resource,
> >   the outbound traffic of these pods is limited, using or sharing one
> >   dedicated Tx queues assigned HTB/TBF/FQ Qdisc. Other kind of pods
> >   (e.g. Pn), the low latency of data access is key. And the traffic is not
> >   limited. Pods use or share other dedicated Tx queues assigned FIFO Qdisc.
> >   This choice provides two benefits. First, contention on the HTB/FQ Qdisc
> >   lock is significantly reduced since fewer CPUs contend for the same queue.
> >   More importantly, Qdisc contention can be eliminated completely if each
> >   CPU has its own FIFO Qdisc for the second kind of pods.
> >
> >   There must be a mechanism in place to support classifying traffic based on
> >   pods/container to different Tx queues. Note that clsact is outside of Qdisc
> >   while Qdisc can run a classifier to select a sub-queue under the
> >   lock.
>
> One alternative, I don't know if it would work for you, it to use the
> net_prio cgroup + mqprio.
>
> Something like this:
>
> * create the cgroup
>   $ mkdir -p /sys/fs/cgroup/net_prio/<CGROUP_NAME>
> * assign priorities to the cgroup (per interface)
>   $ echo "<IFACE> <PRIO>" >> /sys/fs/cgroup/net_prio/<CGROUP_NAME>/net_prio.ifpriomap"
> * use the cgroup in applications that do not set SO_PRIORITY
Yes, I think this is key. In k8s, we can not control the priority of
applications in Pod. and I think 2/2 patch
can provide more mechanisms to select queues from a range.
If possible, you can help me review it.
https://patchwork.kernel.org/project/netdevbpf/patch/20211224164926.80733-3-xiangxia.m.yue@gmail.com/
>   $ cgexec -g net_prio:<CGROUP_NAME> <application>
> * configure mqprio
>   $ tc qdisc replace dev $IFACE parent root handle 100 mqprio \
>       num_tc 3 \
>       map 2 2 1 0 2 2 2 2 2 2 2 2 2 2 2 2 \
>       queues 1@0 1@1 2@2 \
>       hw 0
>
> This would map all traffic with SO_PRIORITY 3 to TX queue 0, for example.
> But I agree that skbedit's queue_mapping not working is unexpected and
> should be fixed.
>
>
> Cheers,
> --
> Vinicius



-- 
Best regards, Tonghao