netdev - Re: [PATCH 2/3][NET_BATCH] net core use batching

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Message-ID: <470AE373.9020207@garzik.org>
Date:	Mon, 08 Oct 2007 22:12:03 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	David Miller <davem@...emloft.net>
CC:	hadi@...erus.ca, peter.p.waskiewicz.jr@...el.com,
	krkumar2@...ibm.com, johnpol@....mipt.ru,
	herbert@...dor.apana.org.au, kaber@...sh.net,
	shemminger@...ux-foundation.org, jagana@...ibm.com,
	Robert.Olsson@...a.slu.se, rick.jones2@...com, xma@...ibm.com,
	gaagaan@...il.com, netdev@...r.kernel.org, rdreier@...co.com,
	mcarlson@...adcom.com, mchan@...adcom.com,
	general@...ts.openfabrics.org, tgraf@...g.ch,
	randy.dunlap@...cle.com, sri@...ibm.com
Subject: Re: [PATCH 2/3][NET_BATCH] net core use batching

David Miller wrote:
> 1) A library for transmit load balancing functions, with an interface
>    that can be made visible to userspace.  I can write this and test
>    it on real multiqueue hardware.
> 
>    The whole purpose of this library is to set skb->queue_mapping
>    based upon the load balancing function.
> 
>    Facilities will be added to handle virtualization port selection
>    based upon destination MAC address as one of the "load balancing"
>    methods.

Groovy.

I'm interested in working on a load balancer function that approximates

	skb->queue_mapping = smp_processor_id()

I'd be happy to code and test in that direction, based on your lib.


> 2) Switch the default qdisc away from pfifo_fast to a new DRR fifo
>    with load balancing using the code in #1.  I think this is kind
>    of in the territory of what Peter said he is working on.
> 
>    I know this is controversial, but realistically I doubt users
>    benefit at all from the prioritization that pfifo provides.  They
>    will, on the other hand, benefit from TX queue load balancing on
>    fast interfaces.

IMO the net driver really should provide a hint as to what it wants.

8139cp and tg3 would probably prefer multiple TX queue behavior to match 
silicon behavior -- strict prio.

And I'll volunteer to write the net driver code for that, if people want 
to see how things would look for that type of hardware packet scheduling.


> 3) Work on discovering a way to make the locking on transmit as
>    localized to the current thread of execution as possible.  Things
>    like RCU and statistic replication, techniques we use widely
>    elsewhere in the stack, begin to come to mind.

Definitely.

	Jeff


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