netdev - Re: Minimizing TCP latency

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Message-Id: <1269876229.2092.3.camel@achroite.uk.solarflarecom.com>
Date:	Mon, 29 Mar 2010 16:23:49 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Ben Hoyt <benhoyt@...il.com>
Cc:	netdev@...r.kernel.org
Subject: Re: Minimizing TCP latency

On Mon, 2010-03-29 at 16:24 +1300, Ben Hoyt wrote:
> > I'm happy to receive some pointers via this list [...]
> 
> Sorry, I should also have posted more about what I've done in terms of
> reducing latency so far:
> 
> * We've already got TCP_NODELAY activated.
> 
> * We've also turned off interrupt coalescing on the network card (for
> example, see http://www.29west.com/docs/THPM/latency-interrupt-coalescing.html).
> 
> * We've modified our process's CPU affinity so it runs on a core by
> itself, reducing interrupt-handling latency slightly further.
> 
> * Our code is written in C, and we've tried to keep it as close to the
> kernel's socket calls as possible.
> 
> So we're currently looking further into ways to reduce latency, which
> currently looks like it'll mean digging deeper into the kernel's
> networking options and innards.

Choose low-latency NICs.  Read the tuning guide, but run your own
benchmarks.

> FYI, we're using RHE release 4 and kernel version 2.6.9 on x86_64 machines.

You're not going to get much help here in working on that kernel.

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare Communications
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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