netdev - Very low latency TCP for clusters

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Date:	Mon, 19 Jul 2010 10:05:19 -0700
From:	Tom Herbert <therbert@...gle.com>
To:	netdev@...r.kernel.org
Subject: Very low latency TCP for clusters

We have been looking at best case TCP latencies that might be achieved
within a cluster (low loss fabric).  The goal is to have latency
numbers roughly comparable to that which can be produced using RDMA/IB
in a low latency configuration  (<5 usecs round trip on netperf TCP_RR
test with one byte data for directly connected hosts as a starting
point).  This would be without changing sockets API, fabric, and
preferably not using TCP offload or a user space stack.

I think there are at least two techniques that will drive down TCP
latency: per connection queues and polling queues.  Per connection
queues (supported by device) should eliminate costs of connection
look-up, hopefully some locking.  Polling becomes viable as core
counts on systems increase, and burning a few CPUs for networking
polling on behalf of very low-latency threads would be reasonable.

Are there any efforts in progress to integrate per connection queues
in the stack or integrate polling of queues?

Thanks,
Tom
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