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From: "David S. Miller" <davem@davemloft.net>
Subject: Re: RFC: NAPI packet weighting patch
Date: Tue, 21 Jun 2005 13:20:44 -0700 (PDT)
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From: Stephen Hemminger <shemminger@osdl.org>
Date: Mon, 06 Jun 2005 21:53:32 -0700

> I noticed that the tg3 driver copies packets less than a certain
> threshold to a new buffer, but e1000 always passes the big buffer up
> the stack. Could this be having an impact?

I bet it does, this makes ACK processing a lot more expensive.  And it
is so much cheaper to just recycle the big buffer back to the chip
if you copy to a small buffer, and it warms up the caches for the
packet headers as a side effect as well.

Actually, it has a _HUGE_ _HUGE_ impact.  If you pass the big buffer
up, the receiving socket gets charged for the size of the huge buffer,
not for just the size of the packet contained within.  This makes
sockets get overcharged for data reception, and it can cause all kinds
of performance problems.

I highly recommend that this gets fixed.