Re: [RFC PATCH v2 0/5] allow overriding default preempt mode from command line

Frederic Weisbecker
2020-10-27T12:22:47Z

On Fri, Oct 09, 2020 at 07:45:54PM +0200, Peter Zijlstra wrote:
> +DEFINE_STATIC_KEY_TRUE(irq_preemption_key);
> +
> +/*
> + * SC:cond_resched
> + * SC:might_resched
> + * SC:preempt_schedule
> + * SC:preempt_schedule_notrace
> + * SB:irq_preemption_key
> + *
> + *
> + * ZERO
> + * cond_resched <- RET0
> + * might_resched <- NOP
> + * preempt_schedule <- NOP
> + * preempt_schedule_notrace <- NOP
> + * irq_preemption_key <- false
> + *
> + * NONE:
> + * cond_resched <- __cond_resched
> + * might_resched <- NOP
> + * preempt_schedule <- NOP
> + * preempt_schedule_notrace <- NOP
> + * irq_preemption_key <- false
> + *
> + * VOLUNTARY:
> + * cond_resched <- __cond_resched
> + * might_resched <- __might_resched
> + * preempt_schedule <- NOP
> + * preempt_schedule_notrace <- NOP
> + * irq_preemption_key <- false
> + *
> + * FULL:
> + * cond_resched <- RET0
> + * might_resched <- NOP
> + * preempt_schedule <- preempt_schedule
> + * preempt_schedule_notrace <- preempt_schedule_notrace
> + * irq_preemption_key <- true
> + */

That's cute! I'll try to end up to that result.

> +static int __init setup_preempt_mode(char *str)
> +{
> + if (!strcmp(str, "zero")) {
> + static_call_update(cond_resched, __static_call_return0);
> + static_call_update(might_resched, (void (*)(void))NULL);
> + static_call_update(preempt_schedule, (void (*)(void))NULL);
> + static_call_update(preempt_schedule_notrace, (void (*)(void))NULL);
> + static_branch_disable(&irq_preemption_key);
> + printk("XXX PREEMPT: %s\n", str);
> + } else if (!strcmp(str, "none")) {
> + static_call_update(cond_resched, __cond_resched);
> + static_call_update(might_resched, (void (*)(void))NULL);
> + static_call_update(preempt_schedule, (void (*)(void))NULL);
> + static_call_update(preempt_schedule_notrace, (void (*)(void))NULL);
> + static_branch_disable(&irq_preemption_key);
> + printk("XXX PREEMPT: %s\n", str);
> + } else if (!strcmp(str, "voluntary")) {
> + static_call_update(cond_resched, __cond_resched);
> + static_call_update(might_resched, __might_resched);
> + static_call_update(preempt_schedule, (void (*)(void))NULL);
> + static_call_update(preempt_schedule_notrace, (void (*)(void))NULL);
> + static_branch_disable(&irq_preemption_key);
> + printk("XXX PREEMPT: %s\n", str);
> + } else if (!strcmp(str, "ponies")) {
> + static_call_update(cond_resched, __cond_resched);
> + static_call_update(might_resched, (void (*)(void))NULL);
> + static_call_update(preempt_schedule, preempt_schedule_thunk);
> + static_call_update(preempt_schedule_notrace, preempt_schedule_notrace_thunk);
> + static_branch_enable(&irq_preemption_key);
> + printk("XXX PREEMPT: %s\n", str);

Why would we need that ponies version?

Thanks!