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

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Message-ID: <20201027122241.GA140902@lothringen>
Date:   Tue, 27 Oct 2020 13:22:41 +0100
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Michal Hocko <mhocko@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Mel Gorman <mgorman@...e.de>,
        Frederic Weisbecker <fweisbecker@...e.de>,
        Ingo Molnar <mingo@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [RFC PATCH v2 0/5] allow overriding default preempt mode from
 command line

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!