netdev - Re: performance issue of netdev_budget and dev

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Date:	Fri, 20 Mar 2009 15:59:42 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	jesse.brandeburg@...el.com
Cc:	hanfang@...du.com, netdev@...r.kernel.org
Subject: Re: performance issue of netdev_budget and dev_weight with ixgbe

From: "Brandeburg, Jesse" <jesse.brandeburg@...el.com>
Date: Fri, 20 Mar 2009 10:27:17 -0700 (Pacific Daylight Time)

> 64 is pretty much the global default for all drivers, not just ixgbe, we 
> didn't "pick" it at all.  at 10 Gb Ethernet speeds, we get a LOT of 
> packets.  When you play with budget you're decreasing the amount of cache 
> coherency you get by handing lots of packets at once.

You're also potentially decreasing fairness with other devices
in the system.

That's the purpose of this value, to allow preemption to other
active NAPI contexts in the current softirq processing run.
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