netdev - Re: qdisc spin lock

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAAmHdhxagKnLP1_5ZW7HTsVBu0TSFYKCvNstAEWN-NHrdnvvVQ@mail.gmail.com>
Date:	Thu, 31 Mar 2016 16:48:43 -0700
From:	Michael Ma <make0818@...il.com>
To:	Cong Wang <xiyou.wangcong@...il.com>
Cc:	Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: qdisc spin lock

I didn't really know that multiple qdiscs can be isolated using MQ so
that each txq can be associated with a particular qdisc. Also we don't
really have multiple interfaces...

With this MQ solution we'll still need to assign transmit queues to
different classes by doing some math on the bandwidth limit if I
understand correctly, which seems to be less convenient compared with
a solution purely within HTB.

I assume that with this solution I can still share qdisc among
multiple transmit queues - please let me know if this is not the case.

2016-03-31 15:16 GMT-07:00 Cong Wang <xiyou.wangcong@...il.com>:
> 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.