Date: Sun, 13 Sep 2009 05:18:46 -0700 (PDT) From: Barney Cordoba <barney_cordoba@yahoo.com> To: freebsd-net@freebsd.org, "rihad@mail.ru >> rihad" <rihad@mail.ru> Subject: Re: [POLLING] strange interrupt/system load Message-ID: <651317.63257.qm@web63901.mail.re1.yahoo.com> In-Reply-To: <4AAB4D56.30207@mail.ru>
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--- On Sat, 9/12/09, rihad <rihad@mail.ru> wrote: > From: rihad <rihad@mail.ru> > Subject: [POLLING] strange interrupt/system load > To: freebsd-net@freebsd.org > Date: Saturday, September 12, 2009, 3:27 AM > The box experiences ~230 mbit/s > traffic flow through it. I've doubled some sysctls after > reading polling(4): > kern.polling.each_burst=10 # was: 5 > kern.polling.burst_max=350 # was: 150 > > FreeBSD 7.2-RELEASE-p3 amd64 > HZ=1000 > > Now for the fun part. > > With kern.polling.idle_poll = 1 top shows: > CPU: 0.0% user, 0.0% nice, 26.9% system, > 3.1% interrupt, 70.0% idle > ~8000 interrupts/s total according to systat -vmstat: > 1999 cpu0: time > 2000 cpu1: time > 1999 cpu2: time > 1999 cpu3: time > > With kern.polling.idle_poll = 0 top shows: > CPU: 0.0% user, 0.0% nice, 0.0% system, > 13.9% interrupt, 86.0% idle > Still the same ~8000 clock interrupts/s. > > Under both scenarios polling is enabled on both em0 and em1 > through ifconfig. > > > 1) Why is the interrupt load relatively high with polling > enabled? > 2) How come 13.9% interrupts are not also in the first > scenario if their total rate is the same (~8000)? > > Thanks. The more important questions are: 1) Why are you polling with a NIC that can be precisely set to interrupt as often or as little as you like? 2) Why do so many people run systems with high network load with AMD64 builds when its significantly slower to do so? Do you have google sized databases so you need 64-bit pointers? As to why you get interrupt load, how do you think that polling is implemented? By Magic? You are merely shifting the interrupt load from the em driver to the software interrupts. Running em drivers with AIM is essentially the same as polling without the associated system overhead that polling introduces. Barney
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