netdev - RE: RFC [PATCH net-2.6 1/6] net: Scheduling softirqs between CPUSs

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Message-ID: <36D9DB17C6DE9E40B059440DB8D95F52049D5CE5@orsmsx418.amr.corp.intel.com>
Date:	Mon, 10 Mar 2008 18:06:30 -0700
From:	"Brandeburg, Jesse" <jesse.brandeburg@...el.com>
To:	"Max Krasnyanskiy" <maxk@...lcomm.com>,
	"David Miller" <davem@...emloft.net>
Cc:	<therbert@...gle.com>, <netdev@...r.kernel.org>,
	"Steven Rostedt" <rostedt@...dmis.org>,
	"Ingo Molnar" <mingo@...e.hu>
Subject: RE: RFC [PATCH net-2.6 1/6] net: Scheduling softirqs between CPUSs

Max Krasnyanskiy wrote:
> David Miller wrote:
>> From: therbert@...gle.com (Tom Herbert)
>> Date: Wed,  5 Mar 2008 12:51:16 -0800 (PST)
>> 
>>> This patch implements kernel changes to allow scheduling of
>>> softirq's between processors. 
>>> 
>>> Signed-off-by: Tom Herbert <therbert@...gle.com>
>> 
>> I've stated this in the past and I still feel that it is foolish to
>> put all of this code into the kernel when every single piece of
>> networking hardware will be doing this for us transparently.
>> 
>> Maybe if someone had proposed this 4 or 5 years ago, but right now
>> this code will be irrelevant by the time it ships to any real users.
> 
> Plus it seems that for this kind of stuff it be better to replace
> network softirq with kthreads (like in -rt kernel) and let the
> scheduler take care of the load balancing. More flexible and scalable.
> I'd suggest for your to play with -rt kernel and see if it already
> does what you need.

Could we use something like this to reschedule NAPI onto other
processors?  If we get unlucky enough to have multiple napi routines
polling on a single CPU, and one or more completely idle CPUs (idle at
least for softirq) then we could really use one or the other of these
solutions.

anyone know how -rt kernels work for high I/O load environments like 10
Gigabit Ethernet?

Jesse
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