Subject: Re: Per-CPU Queueing for QoS

From: Stephen Hemminger <[email-masked]>
Date: Sun, 12 Nov 2017 16:14:31 -0800

On Sun, 12 Nov 2017 13:43:13 -0800
Michael Ma <[email-masked]> wrote:

> Any comments? We plan to implement this as a qdisc and appreciate any early feedback.
> 
> Thanks,
> Michael
> 
> > On Nov 9, 2017, at 5:20 PM, Michael Ma <[email-masked]> wrote:
> > 
> > Currently txq/qdisc selection is based on flow hash so packets from
> > the same flow will follow the order when they enter qdisc/txq, which
> > avoids out-of-order problem.
> > 
> > To improve the concurrency of QoS algorithm we plan to have multiple
> > per-cpu queues for a single TC class and do busy polling from a
> > per-class thread to drain these queues. If we can do this frequently
> > enough the out-of-order situation in this polling thread should not be
> > that bad.
> > 
> > To give more details - in the send path we introduce per-cpu per-class
> > queues so that packets from the same class and same core will be
> > enqueued to the same place. Then a per-class thread poll the queues
> > belonging to its class from all the cpus and aggregate them into
> > another per-class queue. This can effectively reduce contention but
> > inevitably introduces potential out-of-order issue.
> > 
> > Any concern/suggestion for working towards this direction?  

In general, there is no meta design discussions in Linux development
Several developers have tried to do lockless
qdisc and similar things in the past.

The devil is in the details, show us the code.