Cost of enabling ALTQ in kernels

[David Brownlee]

I have a couple of gateway boxes where I want to use ALTQ
(primarily for limited bandwidth to/from certain test
machines). In order to minimise custom kernel proliferation
I'd like to just enable ALTQ in all kernels, but only turn
it on on certain machines.

Is there any significant network performance or other cost
in having ALTQ compiled into the kernel but not used?

[Thor Lancelot Simon]

Post by David Brownlee
I have a couple of gateway boxes where I want to use ALTQ
(primarily for limited bandwidth to/from certain test
machines). In order to minimise custom kernel proliferation
I'd like to just enable ALTQ in all kernels, but only turn
it on on certain machines.
Is there any significant network performance or other cost
in having ALTQ compiled into the kernel but not used?

It certainly makes the kernel considerably larger.

Thor

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[Joerg Sonnenberger]

Post by David Brownlee
Is there any significant network performance or other cost
in having ALTQ compiled into the kernel but not used?

In the current world, yes. It can be improved to do either of:
(1) One additional indirect functoin call per ifq operation.
(2) One additional conditional branch per ifq operation.

The first choice shouldn't increase the size of the kernel (might even
make it a bit smaller), the second would (very) slightly increase it.

Joerg

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