Date: Thu, 20 Jul 2006 09:36:14 -0600 From: Scott Long <scottl@samsco.org> To: Peter Jeremy <peterjeremy@optushome.com.au> Cc: freebsd-stable@freebsd.org, Ed Maste <emaste@phaedrus.sandvine.ca> Subject: Re: How to setup polling on 'bge' interface Message-ID: <44BFA2EE.7060308@samsco.org> In-Reply-To: <20060720112613.GB716@turion.vk2pj.dyndns.org> References: <20060711190908.GC69272@registro.br> <20060720023856.GA65960@sandvine.com> <20060720112613.GB716@turion.vk2pj.dyndns.org>
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Peter Jeremy wrote: > On Wed, 2006-Jul-19 22:38:56 -0400, Ed Maste wrote: > >>- You may have to adjust some parameters in the kern.polling sysctl >> tree - specifically, kern.polling.burst_max, kern.polling.each_burst >> and kern.polling.user_frac might need tweaking. > > > Note that increasing kern.polling.burst_max and kern.polling.each_burst > will also increase the number of soft interrupts. > > >>- The polling feedback algorithm does not work very well if your >> workload is focused largely on per-packet tasks (such as routing or >> bridging). You'll find that there is still idle CPU time at the >> point you start dropping packets. I have some work in progress to >> address this, but it's not yet committed. > > > I thought setting kern.polling.idle_poll would allow the CPU to > utilise all idle time. The downside is that the system always shows > as 100% utilised so it's very difficult to know how busy the system > actually is. > > >>- Polling's major advantage is the avoidance of livelock on UP systems, >> and not improved performance. > > > The limited testing I've done on a Sun V20z at work suggests that you > can get better routing throughput in interrupt mode than polling mode. > YMMV and this is before tweaking the polling parameters. (My testing > also suggests that I don't really need to do any tweaking because > the limiting factor is the gigabit interfaces rather than the V20z). > This might not apply to bge, but the adaptive polling + fast interrupt changes that I made to if_em earlier in the year were a huge win over the standard polling code in terms of CPU utilization and packets per second. I think it also survived a load that caused normal polling to essentially livelock the machine. And, it had the advantage of automatically adapting to bursty loads. Scotthome | help
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