Kernel Click Scheduling

[Nickolai Zeldovich]

> How is Click scheduled in-kernel?  The reason I ask is I have a
> CPU-bound Click configuration (InfiniteSource to discard, no queuing),
> and it runs 10% faster in usermode click than kernel click on the same
> machine!  I'm wondering if it has to do with scheduling latencies, or if
> I should be looking elsewhere.

I believe the Linux kernel module will call the scheduler every N
iterations (DRIVER_ITER_LINUXSCHED in routerthread.c) so if your
configuration takes very little CPU time per iteration, it might
be calling the scheduler much more often than a user-space config
(where the scheduler only gets called at a frequency of HZ.)

You might try increasing the DRIVER_ITER_LINUXSCHED value to see
if this is actually the case or I'm just making this up :-)

-- kolya