netdev - Re: [RFC v2: Patch 1/3] net: hand off skb list to other cpu to submit to upper layer

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Date:	Fri, 13 Mar 2009 17:24:10 -0700
From:	Tom Herbert <therbert@...gle.com>
To:	David Miller <davem@...emloft.net>
Cc:	yanmin_zhang@...ux.intel.com, bhutchings@...arflare.com,
	andi@...stfloor.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, herbert@...dor.apana.org.au,
	jesse.brandeburg@...el.com, shemminger@...tta.com
Subject: Re: [RFC v2: Patch 1/3] net: hand off skb list to other cpu to submit 
	to upper layer

>> I appreciate this philosophy, but unfortunately I don't have the
>> luxury of working with a NIC that solves these problems.  The reality
>> may be that we're trying to squeeze performance out of crappy hardware
>> to scale on multi-core.  Left alone we couldn't get the stack to
>> scale, but with these "destable hacks" we've gotten 3X or so
>                         ^^^^^^^^
>
> Spelling.
>
>> improvement in packets per second across both our dumb 1G and 10G
>> NICs
>
> Do these NICs at least support multiqueue?
>

Yes, we are using a 10G NIC that supports multi-queue.  The number of
RX queues supported is half the number of cores on our platform, so
that is going to limit the parallelism.  With multi-queue turned on we
do see about 4X improvement in pps over just using a single queue;
this is about the same improvement we see using a single queue with
our software steering techniques (this particular device provides the
Toeplitz hash).  Enabling HW multi-queue has somewhat higher CPU
utilization though, the extra device interrupt load is not coming for
free.  We actually use the HW multi-queue in conjunction with our
software steering to get maximum pps (about 20% more).
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