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Re: RFC: NAPI packet weighting patch

To: Leonid Grossman <leonid.grossman@xxxxxxxxxxxx>
Subject: Re: RFC: NAPI packet weighting patch
From: Andi Kleen <ak@xxxxxxx>
Date: Thu, 23 Jun 2005 01:13:00 +0200
Cc: "'David S. Miller'" <davem@xxxxxxxxxxxxx>, ak@xxxxxxx, hadi@xxxxxxxxxx, becker@xxxxxxxxx, rick.jones2@xxxxxx, netdev@xxxxxxxxxxx, davem@xxxxxxxxxx
In-reply-to: <200506222242.j5MMgbxS009935@xxxxxxxxxxxxxxxxx>
References: <20050622.132241.21929037.davem@xxxxxxxxxxxxx> <200506222242.j5MMgbxS009935@xxxxxxxxxxxxxxxxx>
Sender: netdev-bounce@xxxxxxxxxxx
> This is very hw-dependent, since there are NICs that read descriptors in
> batches anyways - but the second argument below is compelling.

The computing time must be quite long to be really a win.
You need to waste a few hundred cycles at least on a modern fast CPU.

> > 
> > 2) As shown above, it gives you compute time which can be used to
> >    schedule the prefetch.  This nearly makes RX replenishment free.
> >    Instead of having the CPU spin on a cache miss when we run
> >    eth_type_trans() during those cycles, we do useful work.

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