netdev - Re: qdisc spin lock

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Date:	Thu, 31 Mar 2016 15:16:22 -0700
From:	Cong Wang <xiyou.wangcong@...il.com>
To:	Michael Ma <make0818@...il.com>
Cc:	Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: qdisc spin lock

On Wed, Mar 30, 2016 at 12:20 AM, Michael Ma <make0818@...il.com> wrote:
> As far as I understand the design of TC is to simplify locking schema
> and minimize the work in __qdisc_run so that throughput won’t be
> affected, especially with large packets. However if the scenario is
> that multiple classes in the queueing discipline only have the shaping
> limit, there isn’t really a necessary correlation between different
> classes. The only synchronization point should be when the packet is
> dequeued from the qdisc queue and enqueued to the transmit queue of
> the device. My question is – is it worth investing on avoiding the
> locking contention by partitioning the queue/lock so that this
> scenario is addressed with relatively smaller latency?

If your HTB classes don't share bandwidth, why do you still make them
under the same hierarchy? IOW, you can just isolate them either with some
other qdisc or just separated interfaces.