netdev - Re: Per-CPU Queueing for QoS

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Date:   Sun, 12 Nov 2017 13:43:13 -0800
From:   Michael Ma <make0818@...il.com>
To:     Linux Kernel Network Developers <netdev@...r.kernel.org>
Cc:     jianjun.duan@...baba-inc.com, xiangning.yu@...baba-inc.com
Subject: Re: Per-CPU Queueing for QoS

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 <make0818@...il.com> 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?