Skip site navigation (1)Skip section navigation (2)
Date:      Mon, 26 Sep 2011 09:17:43 -0400
From:      John Baldwin <jhb@freebsd.org>
To:        freebsd-current@freebsd.org
Cc:        Adrian Chadd <adrian@freebsd.org>, Alexander Motin <mav@freebsd.org>
Subject:   Re: ath / 802.11n performance issues and timer code
Message-ID:  <201109260917.44236.jhb@freebsd.org>
In-Reply-To: <CAJ-Vmo=kScoove4_dvj_-LS%2BWnWhF4aWU9FrWF4=5kYr06-AoA@mail.gmail.com>
References:  <CAJ-VmomZyDJV62yCQOvG=UB6H4wfz9=3_cWzEL7vWAA14TCyYA@mail.gmail.com> <4E7D6700.4080302@FreeBSD.org> <CAJ-Vmo=kScoove4_dvj_-LS%2BWnWhF4aWU9FrWF4=5kYr06-AoA@mail.gmail.com>

next in thread | previous in thread | raw e-mail | index | archive | help
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



Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?201109260917.44236.jhb>