Re: [PATCH] hrtimer: Replace cpu_base->active_bases with a direct check of the active list

On Thu, Apr 09, 2015 at 09:20:39AM +0200, Ingo Molnar wrote:

if at least one base is active (on my fairly standard system all cpus have at least one active hrtimer base all the time - and many cpus have two bases active), then we run hrtimer_get_softirq_time(), which dirties the cachelines of all 4 clock bases:

    base->clock_base[HRTIMER_BASE_REALTIME].softirq_time = xtim;
    base->clock_base[HRTIMER_BASE_MONOTONIC].softirq_time = mono;
    base->clock_base[HRTIMER_BASE_BOOTTIME].softirq_time = boot;
    base->clock_base[HRTIMER_BASE_TAI].softirq_time = tai;

so in practice we not only touch every cacheline in every timer interrupt, but we _dirty_ them, even the inactive ones.

Urgh we should really _really_ kill that entire softirq mess.

All it needs it hrtimer_start*() returning -ENOTIME when it cannot queue the timer.

Of course, all that needs it auditing all hrtimer_start*() callsites, which is a lot of work.