On Thu, 28 Jun 2012 20:00:55 +0800
Junchang Wang <[email protected]> wrote:

> Hi Emil and list,
> 
> 
> > >
> > >I asked Luigi Rizzo for help, whom is the author of netmap, told me
> > >that I have too many cores in the machine and it should work if I tell
> > >ixgbe use less cores (2 to 4 is ok).
> >
> > You can limit the number of queues by using the RSS module parameter.
> > This parameter only exists on the out-of-tree driver from SF:
> >
> > insmod ./ixgbe.ko RSS=2
> >
> >
> I encountered a similar problem, and we got a significant performance boost
> after limiting the number of queues from 64 to 8. (The sever is equipped
> with 80 cores.)
> 
> I'm very curious about what happened. More queues can amortize the work
> load and help programs use more CPU cores and cache. But why limiting the
> number of queues get better performance? Can one of you shed light on this?
> 
> Thanks.
> 

More queues means the hardware has to poll more rings and increases
the PCI bus bandwidth. 

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