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Re: bad TSO performance in 2.6.9-rc2-BK

To: "David S. Miller" <davem@xxxxxxxxxxxxx>
Subject: Re: bad TSO performance in 2.6.9-rc2-BK
From: Nivedita Singhvi <niv@xxxxxxxxxx>
Date: Wed, 22 Sep 2004 13:56:17 -0700
Cc: ak@xxxxxxx, anton@xxxxxxxxx, netdev@xxxxxxxxxxx
In-reply-to: <20040922133011.5885640b.davem@xxxxxxxxxxxxx>
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David S. Miller wrote:

The former rarely goes faster with TSO enabled simply
because there is sufficient cpu and bus bandwidth to
keep the card full.

At about 700MHz (ok, old, I know) or thereabouts, it
usually took > 1 CPU to drive a gigabit card, iirc,
about 1.5 CPUs or so.

Whereas with something like SpecWEB the extra cpu and
bus cycles are needed by other resources of the benchmark
and thus performance goes up.


I have no idea why people think TSO will make some single
stream TCP test go faster, it doesn't buy you more bytes
on the wire :-)

True, if the card was already doing line speed,
no, as you say, it won't help making the stack go
faster :). If not, though, the gain in doing only
one pass down the stack, one route look up, etc in
place of multiple handoffs should help, correct?


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