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Re: RFC: NAPI packet weighting patch

To: Mitch Williams <mitch.a.williams@xxxxxxxxx>
Subject: Re: RFC: NAPI packet weighting patch
From: Ben Greear <greearb@xxxxxxxxxxxxxxx>
Date: Mon, 06 Jun 2005 17:08:57 -0700
Cc: "Ronciak, John" <john.ronciak@xxxxxxxxx>, "David S. Miller" <davem@xxxxxxxxxxxxx>, mchan@xxxxxxxxxxxx, hadi@xxxxxxxxxx, buytenh@xxxxxxxxxxxxxx, jdmason@xxxxxxxxxx, shemminger@xxxxxxxx, netdev@xxxxxxxxxxx, Robert.Olsson@xxxxxxxxxxx, "Venkatesan, Ganesh" <ganesh.venkatesan@xxxxxxxxx>, "Brandeburg, Jesse" <jesse.brandeburg@xxxxxxxxx>
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Organization: Candela Technologies
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Mitch Williams wrote:

On Mon, 6 Jun 2005, Ronciak, John wrote:

        If you force the e1000 driver to do RX replenishment every N
        packets it should reduce the packet drops the same (in the
        single NIC case) as if you reduced the dev->weight to that
        same value N.

But this isn't what we are seeing.  Even if we just reduce the weight
value to 32 from 64, all of the drops go away.  So there seems to be
other things affecting this.

Some quickie results for everybody -- I've been working on other stuff this
morning and haven't had much time in the lab.

Increasing the RX ring to 512 descriptors eliminates dropped packets, but
performance goes down.  When I mentioned this, John and Jesse both nodded
and said, "Yep.  That's what happens when the descriptor ring grows past
one page."

Reducing the weight to 32 got rid of almost all of the dropped packets
(down to < 1 per second); reducing it to 20 eliminated all of them.  In
both cases performance rose as compared to the default weight of 64.

Tests were run on 2.6.12rc5 on a dual Xeon 2.8GHz PCI-X system.  We run
Chariot for performance testing, using TCP/IP large file transfers with 10
Windows 2000 clients.

So is the Linux server reading/writing these large files to/from the disk?

Can you tell us how much performance went down when you increased the
descriptors to 512?


Ben Greear <greearb@xxxxxxxxxxxxxxx>
Candela Technologies Inc

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