Re: [RFC] irq rate limit

[Keir Fraser <keir.fraser@eu.citrix.com>]

On 09/09/2009 10:07, "Qing He" <qing.he@intel.com> wrote:

>> What's the generation counter for? Why not just zero desc->rl_cnt in the
>> timer handler?
> 
> If zeroing desc->rl_cnt in the timer handler, we have to zero that of
> all irqs. If the numbers of possible irqs is big or sparse, it's a bit
> painful.

Ah yes, I see. An always-on 10ms timer is ugly however. The Intel guys
working on power management won't like it as it will reduce deep-sleep
residency.

I would suggest getting rid of the generation counter and enable the timer
only when the irq_ratelimit_list is non-empty. In do_IRQ(), when rl_cnt
exceeds the threshold:
 now = NOW();
 if ( now < (desc->rl_quantum_start + MILLISECS(10)) )
    Add to irq_ratelimit_list; Kick timer if list was previously empty;
 else
    desc->rl_cnt = 0; desc->rl_quantum_start = now;

And in the timer handler, for each desc on the list:
 desc->rl_cnt = 0; desc->rl_quantum_start = now;

And at the end of the timer handler, do not set_timer().

This approach adds the overhead of get_s_time() every
irq_ratelimit_threshold interrupts, which should be unmeasurably tiny.

 -- Keir