Add support for batching interrupts in system interrupt code

[• hselasky]

Summary

Implement intr_handler_needs_execution() to serve the purpose of allowing high-frequency interrupts to be batched.
By calling intr_handler_needs_execution() the driver acknowledge interrupts that occurred after the invocation of the current interrupt handler call.

This change basically reverts r357004.

Interrupt handlers can do batching like this:

static void interrupt_handler(void *arg)
{
  int to = 1000;

  do {
       /* interrupt code */
   } while (to-- && intr_handler_needs_execution(ih_cookie));
}

Sponsored by: Mellanox Technologies

[• hselasky]

Fix compilation issue and make sure network epoch is available when used!

[gallatin]

Some feedback:

• This essentially removes the epoch optimization from all network drivers because it becomes opt-in, rather than automatic. I don't like that
• You've replaced a flag with an 8 byte field in a struct which can be touched hundreds of thousands or millions of times per second. I don't like that.
• You've removed interrupt storm epoch hogging protection. I don't like that.

To do what you want, can you instead make a negative flag for opting opt and leave most the rest of the code intact?

[• hselasky]

Hi,

This essentially removes the epoch optimization from all network drivers because it becomes opt-in, rather than automatic. I don't like that

Yes, this feature should be op-in until someone sits down and fixes all the network driver's input paths.

FreeBSD is a general purpose operating system. It shall not only be hard-optimised for network drivers, like the patch Gleb S. made.
There might be more subsystems which want another epoch than the network epoch and my patch addresses that.

You've replaced a flag with an 8 byte field in a struct which can be touched hundreds of thousands or millions of times per second. I don't like that.

This field should not be touched more than 8k times per second. Else you have a network card you should not use for heavy network traffic or you have not tuned the RX queues appropriately.

You've removed interrupt storm epoch hogging protection. I don't like that.

The epoch wrapper should be per-interrupt function call and that's it.

To do what you want, can you instead make a negative flag for opting opt and leave most the rest of the code intact?

I disagree.

[kib]

To add some colors to the discussion, I disagree with both approaches. My main complain is that *net epoch* should not be married with the interrupts handlers infrastructure, neither in code nor in data. I agree with people that mark this as layering violations.

If you want automatic epoch enter, with possible rate or interval limiting, you need a hooks that are executed before and after the thread handler loop is performed. We already have examples of such hooks with pre- and post- filter and ithread hooks.

And yes, it should be opt-in and not automatic on INTR_TYPE_NET

[• hselasky]

Implement feedback.

[• hselasky]

Minor compile fix.