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From: John Baldwin <jhb@freebsd.org>
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	(bigwig.baldwin.cx); Mon, 26 Sep 2011 10:00:54 -0400 (EDT)
Cc: Adrian Chadd <adrian@freebsd.org>, Alexander Motin <mav@freebsd.org>
Subject: Re: ath / 802.11n performance issues and timer code
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On Sunday, September 25, 2011 5:48:31 am Adrian Chadd wrote:
> Nope, it has the opposite effect:
> 
> * Increased latency may make aggregation better (for TX) but it limits
> throughput because TCP senses a latency increase;

I suspect this matters more.  Have you tried comparing UDP throughput in the 
two cases?

One behavioral difference of a periodic timer vs a deadline timer is that if 
you ask to delay for "1 clock tick", that can be anywhere from 0us to 1000us 
(with hz == 1000) when using the periodic timer (because you can set the 
callout at any time within a tick, but the callout will fire at the start of 
the next tick).  However, for a deadline timer, the TCP timer will always fire 
1000us after you set the timer.

-- 
John Baldwin