FreeBSD as a gigabit router

Vladimir Ivanov wawa at
Wed Oct 10 09:12:23 PDT 2007

Ed Maste wrote:
> On Thu, Oct 04, 2007 at 12:02:56PM -0700, Michael DeMan wrote:
>> Also, we've noticed at least on FBSD 6.x that there seem to be very  
>> few advantages in using polling on network interfaces.  We still run  
>> it, so that we have responsive SSH/BGP/OSPF processes on the  
>> machines, but my testing has shown that for sheer throughput, there  
>> is basically no difference.  I'd be curious if anybody knows the  
>> scoop on this.
>> The polling mechanism includes a feedback mechanism that attempts to
>> keep a certain amount of CPU time available for userland.  It works
>> well at keeping the system usable under high load, but it doesn't
>> perform so well if you want to dedicate most of the CPU time to polling
>> in order to get near the maximum throughput.
JFYI: We've used another trick. Yandex's driver allows to alter RX' 
threads priority.  Also, it disables interrupts if driver busy (and 
works like a polling).  This combination seems to be very stable under 
heavy load.
Also, I seem it more intuitive for tuning.
> I have some prototype code that addresses this, and the the throughput
> with the new polling algorithm beat the non-polling kernel perf. by a
> small margin.  This won't make it into RELENG_7, but I plan to bring
> it to HEAD at some point.
> -Ed
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Vladimir Ivanov
Network Operations Center
OOO "Yandex"
t: +7 495 739-7000
f: +7 495 739-7070
@: noc at (corporate)
  wawa at (personal)

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