Messages in this thread | | | Date | Tue, 27 Oct 2020 13:28:41 +0100 | From | Peter Zijlstra <> | Subject | Re: [RFC PATCH v2 0/5] allow overriding default preempt mode from command line |
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On Tue, Oct 27, 2020 at 01:22:41PM +0100, Frederic Weisbecker wrote: > 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.
Beware, ZERO is 'broken', I included it because I was curious what, if anything, would happen :-)
> > +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?
We don't, but it was a missing combination (like ZERO), and I wanted to test it worked (as expected, it does).
We'll only encounter it as an intermediate state when flipping states at runtime, but unlike zero, it should work just fine.
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