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Re: issue with new TCP TSO stuff

To: "David S. Miller" <davem@xxxxxxxxxxxxx>
Subject: Re: issue with new TCP TSO stuff
From: Andi Kleen <ak@xxxxxx>
Date: Thu, 12 May 2005 16:13:05 +0200
Cc: netdev@xxxxxxxxxxx
In-reply-to: <20050511.223036.39664020.davem@xxxxxxxxxxxxx> (David S. Miller's message of "Wed, 11 May 2005 22:30:36 -0700 (PDT)")
References: <20050511.223036.39664020.davem@xxxxxxxxxxxxx>
Sender: netdev-bounce@xxxxxxxxxxx
User-agent: Gnus/5.110002 (No Gnus v0.2) Emacs/21.3 (gnu/linux)
"David S. Miller" <davem@xxxxxxxxxxxxx> writes:
> This shows up in testing where the connection is application limited.
> For example, an "scp" goes more slowly over TSO now, there are less
> cpu cycles available for the encryption.
> It's tricky to come up with a scheme to fix this.  I would love to be
> able to not do the page grabs/releases in the actual TSO frame.  I
> really haven't come up with a clean way to do that however.

Are you sure a few atomic_inc/dec are really causing noticeable
slowdown? That would surprise me unless you have lots of cache line
bouncing on a MP system.

What CPU did you test it on? Does it happen with only a single CPU?
And did you actually see them in some profile?

Assuming the struct page is in cache the P4 core is the slowest at
that that I know, but even on that one it should be in the noise on
the other overhead of talking to a NIC on a PCI bus.

Perhaps it is something else..


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