linux-kernel - Re: [RFC PATCH v3 1/3] sched/isolation: Add infrastructure for dynamic CPU isolation

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Message-ID: <87jzeqyh3d.ffs@tglx>
Date: Wed, 02 Oct 2024 11:44:22 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: Costa Shulyupin <costa.shul@...hat.com>, longman@...hat.com,
 ming.lei@...hat.com, pauld@...hat.com, juri.lelli@...hat.com,
 vschneid@...hat.com, Michael Ellerman <mpe@...erman.id.au>, Nicholas
 Piggin <npiggin@...il.com>, Christophe Leroy
 <christophe.leroy@...roup.eu>, Naveen N Rao <naveen@...nel.org>, Zefan Li
 <lizefan.x@...edance.com>, Tejun Heo <tj@...nel.org>, Johannes Weiner
 <hannes@...xchg.org>, Michal Koutný <mkoutny@...e.com>,
 Ingo Molnar
 <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>, Vincent Guittot
 <vincent.guittot@...aro.org>, Dietmar Eggemann <dietmar.eggemann@....com>,
 Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>, Mel
 Gorman <mgorman@...e.de>, Costa Shulyupin <costa.shul@...hat.com>, Bjorn
 Helgaas <bhelgaas@...gle.com>, linuxppc-dev@...ts.ozlabs.org,
 linux-kernel@...r.kernel.org, cgroups@...r.kernel.org
Subject: Re: [RFC PATCH v3 1/3] sched/isolation: Add infrastructure for
 dynamic CPU isolation

On Mon, Sep 16 2024 at 15:20, Costa Shulyupin wrote:
> +/*
> + * housekeeping_update - change housekeeping.cpumasks[type] and propagate the
> + * change.
> + */
> +static int housekeeping_update(enum hk_type type, const struct cpumask *update)
> +{
> +	struct {
> +		struct cpumask changed;
> +		struct cpumask enable;
> +		struct cpumask disable;
> +	} *masks;
> +
> +	masks = kmalloc(sizeof(*masks), GFP_KERNEL);
> +	if (!masks)
> +		return -ENOMEM;
> +
> +	lockdep_assert_cpus_held();
> +	cpumask_xor(&masks->changed, housekeeping_cpumask(type), update);
> +	cpumask_and(&masks->enable, &masks->changed, update);
> +	cpumask_andnot(&masks->disable, &masks->changed, update);
> +	cpumask_copy(housekeeping.cpumasks[type], update);
> +	WRITE_ONCE(housekeeping.flags, housekeeping.flags | BIT(type));

So this sets the bit for the type

> +	if (!static_branch_unlikely(&housekeeping_overridden))
> +		static_key_enable_cpuslocked(&housekeeping_overridden.key);

What's the point of doing this on every iteration?

> +	kfree(masks);
> +
> +	return 0;
> +}
> +
>  static int __init housekeeping_setup(char *str, unsigned long flags)
>  {
>  	cpumask_var_t non_housekeeping_mask, housekeeping_staging;
> @@ -327,8 +357,11 @@ int housekeeping_exlude_isolcpus(const struct cpumask *isolcpus, unsigned long f
>  		/*
>  		 * Reset housekeeping to bootup default
>  		 */
> +
> +		for_each_clear_bit(type, &boot_hk_flags, HK_TYPE_MAX)
> +			housekeeping_update(type, cpu_possible_mask);

Even for those which are clear

>  		for_each_set_bit(type, &boot_hk_flags, HK_TYPE_MAX)
> -			cpumask_copy(housekeeping.cpumasks[type], boot_hk_cpumask);
> +			housekeeping_update(type, boot_hk_cpumask);
>  
>  		WRITE_ONCE(housekeeping.flags, boot_hk_flags);

Just to overwrite them with boot_hk_flags afterwards. That does not make
any sense at all.

Thanks,

        tglx