Polling slows down bandwidth

[Chuck Swiger]

On Oct 28, 2010, at 11:39 PM, Коньков Евгений wrote:
> Здравствуйте, Chuck.

Um, greetings?  

> Вы писали 28 октября 2010 г., 23:41:58:
> 
> CS> On Oct 28, 2010, at 1:21 PM, Коньков Евгений wrote:
>>> [ ... ]
> 
> CS> What is "sysctl kern.clockrate", and have you increased kern.hz
> CS> in /boot/loader.conf to at least 1000, if not 2000 or 4000?
> 
> # vmstat -i
> interrupt                          total       rate
> irq14: ata0                       193948          6
> irq16: rl0                      42829515       1464
> irq23: nfe0                     41224044       1409
> cpu0: timer                     58494158       1999
> irq256: igb0                      106911          3
> irq257: igb0                      254606          8
> irq258: igb0                           2          0
> Total                          143103184       4892
> 
> # sysctl kern.clockrate
> kern.clockrate: { hz = 1000, tick = 1000, profhz = 2000, stathz = 133 }
> 
> # sysctl kern.hz
> kern.hz: 1000
> but I have configured and installed kern with 2000HZ
> "systat -v" shows that: 2002 cpu0: time

Actually, the interrupt rate is tracking profile hz, which is roughly double the actual kern.hz-- per sysctl, you should try to at least double kern.hz.

> 
> CS> Polling mode operation generally performs better when using older
> CS> 100Mbs ethernet NICs which do not support interrupt mitigation and
> CS> various capabilities like TSO4; gigabit ethernet NICs are smarter
> CS> hardware and can generally outperform polling mode.
> 
> so using polling on gigabit NICs is a bottle neck? and is cause of low performance, is not?

Simple answer is yes.  It should be possible that you could tune polling to get similar performance, or at least better performance than you see now, but the additional hardware capabilities of gigabit NICs are likely to outperform polling mode, just as polling mode can generally outperform old 100MBs ethernet NICs.

Regards,
-- 
-Chuck