Driver performace "Kernel Mode" and "Module Mode"?

Hi all,

I have a strange problem describes as follows:

I have wrote a network device driver and
tried to test its performance by using Smartbit.

The driver performance is 18 Mbps when I use "insmod driver.o".
But it is 22 Mbps when I use this driver as "built-in kernel driver".

Why the performance result between "Module" and "Kernel" is different?

Does this result reasonable?

I need your suggestions. Thank you!

Regards,
Perry.

Perry Wu wrote:
> Hi all,
>
> I have a strange problem describes as follows:
>
> I have wrote a network device driver and
> tried to test its performance by using Smartbit.
>
> The driver performance is 18 Mbps when I use "insmod driver.o".
> But it is 22 Mbps when I use this driver as "built-in kernel driver".
>
> Why the performance result between "Module" and "Kernel" is different?
>
> Does this result reasonable?
>
> I need your suggestions. Thank you!

It can happen because module reference's end up a different TLB and
get called through an indirect linkage. Sort of the same overhead
as DLL or COM.