igb and ALTQ in 9.1-rc3

[Ermal Luçi]

On Tue, Dec 11, 2012 at 3:56 PM, Karim Fodil-Lemelin <
fodillemlinkarim at gmail.com> wrote:

> On 11/12/2012 9:15 AM, Ermal Luçi wrote:
>
>> On Tue, Dec 11, 2012 at 2:05 PM, Barney Cordoba <barney_cordoba at yahoo.com
>> >**wrote:
>>
>>
>>> --- On Tue, 12/11/12, Gleb Smirnoff <glebius at FreeBSD.org> wrote:
>>>
>>>  From: Gleb Smirnoff <glebius at FreeBSD.org>
>>>> Subject: Re: igb and ALTQ in 9.1-rc3
>>>> To: "Jack Vogel" <jfvogel at gmail.com>
>>>> Cc: "Clement Hermann (nodens)" <nodens2099 at gmail.com>, "Barney Cordoba"
>>>>
>>> <barney_cordoba at yahoo.com>, freebsd-net at FreeBSD.org
>>>
>>>> Date: Tuesday, December 11, 2012, 2:58 AM
>>>> On Mon, Dec 10, 2012 at 03:31:19PM
>>>> -0800, Jack Vogel wrote:
>>>> J> UH, maybe asking the owner of the driver would help
>>>> :)
>>>> J>
>>>> J> ... and no, I've never been aware of doing anything to
>>>> stop supporting altq
>>>> J> so you wouldn't see any commits. If there's something
>>>> in the altq code or
>>>> J> support (which I have nothing to do with) that caused
>>>> this no-one informed
>>>> J> me.
>>>>
>>>> Switching from if_start to if_transmit effectively disables
>>>> ALTQ support.
>>>>
>>>> AFAIR, there is some magic implemented in other drivers that
>>>> makes them
>>>> modern (that means using if_transmit), but still capable to
>>>> switch to queueing
>>>> mode if SIOCADDALTQ was casted upon them.
>>>>
>>>>  It seems pretty difficult to say that something is compatible with
>>> something else if it hasn't been tested in a few years.
>>>
>>> It seems to me that ATLQ is the one that should handle if_transmit.
>>> although it's a good argument for having a raw "send" function in
>>> drivers. Ethernet drivers don't need more than a send() routing that
>>> loads a packet into the ring. The decision on what to do if you can't
>>> queue a packet should be in the  network layer, if we must still call
>>> things layers.
>>>
>>> "start" is a leftover from a day when you stuffed a buffer and waited
>>> for an interrupt to stuff in another. The whole idea is antiquated.
>>>
>>> Imagine drivers that pull packets off of a card and simply queue it;
>>> and that you simply submit a packet to be queued for transmit. Instead
>>> of trying to find 35 programmers that understand all of the lock BS,
>>> you only need to have a couple.
>>>
>>> I always disable all of the gobbledegook like checksum offloading. They
>>> just muddy the water and have very little effect on performance. A modern
>>> cpu can do a checksum as fast as you can manage the "capabilities"
>>> without
>>> disrupting the processing path.
>>>
>>> With FreeBSD, every driver is an experience. Some suck so bad that they
>>> should come with a warning. The MSK driver is completely useless, as
>>> an example.
>>>
>>>
>>> BC
>>> ______________________________**_________________
>>> freebsd-net at freebsd.org mailing list
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>>> "
>>>
>>>  During implementation of if_transmit altq was not considered at all.
>> The default if_transmit provides some compatibility but that is void since
>> altq has not been converted to call if_transmit after processing the mbuf.
>>
>> ALTQ can be adapted quite easily to if_transmit model it just wasn't done
>> at the time.
>> With if_transmit model it can even be modularized and not be a compile
>> kernel option since the queue of the iface is abstracted now.
>>
>> I have always wanted to do a diff but have not yet got to it.
>> The change is quite simple just provide an altq_transmit default method
>> and
>> just hook into if_transmit model on the fly.
>> You surely need to handle some iface events and enable altq based on
>> request but its is not a hard to implement.
>>
>> I will always have this in my TODO but not sure when i can get to it.
>>
>>  The issue is not only that igb doesn't support if_transmit or if_start
> method but that ALTQ isn't multiqueue ready and still uses the IFQ_LOCK for
> all of its enqueue/dequeue operations. A simple drop in of if_transmit is
> bound to cause race conditions on any multiqueue driver with ALTQ.
>
> I do have a patch set for this on igb but its ugly and needs more work
> although it should get you going. Let me know if your interested I will
> clean it up and send it over. For more information on ALTQ discussion and
> igb please read this thread: http://freebsd.1045724.n5.**
> nabble.com/em-igb-if-transmit-**drbr-and-ALTQ-td5760338.html<http://freebsd.1045724.n5.nabble.com/em-igb-if-transmit-drbr-and-ALTQ-td5760338.html>
>
> Best regards,
>
> Karim.
>
>
ALTQ needs to do serialization of packets to apply its policy.
While it can be extended to map driver queues to ALTQ queues that is not
easy done without getting some interface to the driver to communicate.
The poor man implementation would be to pass an index argument when calling
driver transmit routine.


>
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> "
>



-- 
Ermal