From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andi Kleen Subject: Re: issue with new TCP TSO stuff Date: Thu, 12 May 2005 16:13:05 +0200 Message-ID: References: <20050511.223036.39664020.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: netdev@oss.sgi.com Return-path: To: "David S. Miller" In-Reply-To: <20050511.223036.39664020.davem@davemloft.net> (David S. Miller's message of "Wed, 11 May 2005 22:30:36 -0700 (PDT)") Sender: netdev-bounce@oss.sgi.com Errors-to: netdev-bounce@oss.sgi.com List-Id: netdev.vger.kernel.org "David S. Miller" 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.. -Andi