Re: [Codel] [RFC] ath10k: implement dql for htt tx

[Ben Greear <greearb@candelatech.com>]

On 03/30/2016 02:22 AM, Michal Kazior wrote:
> On 29 March 2016 at 17:54, Ben Greear <greearb@candelatech.com> wrote:
>> On 03/29/2016 12:49 AM, Michal Kazior wrote:
>>
>>>> if you are getting a pure codel result of 160ms, that means the
>>>> implementation is broken. But I think (after having read your
>>>> description twice), the baseline result today of 160ms of queuing was
>>>> with a fq_codel *qdisc* doing the work on top of huge buffers,
>>>
>>>
>>> Yes. The 160ms is with fq_codel qdisc with ath10k doing DQL at 6mbps.
>>> Without DQL ath10k would clog up all tx slots (1424 of them) with
>>> frames. At 6mbps you typically want/need a handful (5-10) of frames to
>>> be queued.
>>
>>
>> Have you actually verified you can use all tx slots?
>
> It works in most cases. I guess you're suspecting some of your
> tx(flushing?) problems might be induced by overcommiting?
>
>> The way the
>> firmware uses it's tx buffers I think you may not be able to actually
>> do that...and in practice, you will get a lot fewer usable tx-buffers
>> than configured....
>
> Could be, e.g. I'm aware management frames are kind of a special case
> in recent firmware revisions.
>
> What would/do you expect firmware would/will do when we overcommit?
> The driver does advertise number of HTT tx slots so I would expect it
> to work fine if it didn't crash during boot.

The firmware will return something like tx-dropped immediately.  The reason
is that the firmware keeps more than one internal priority queue, and in general, reserves
some of the tx-descriptors for high priority.

So, you never see tx-queues completely full in the driver, so tx queues are
not stopped farther up the stack.

Possibly I am confused about some of this, so I'm quite curious if you ever see
tx-queues determined to be full in the ath10k driver.

Thanks,
Ben

-- 
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc  http://www.candelatech.com