Re: [PATCH v2 1/9] KVM: arm/arm64: vgic: Add LPI translation cache definition

[Julien Thierry <julien.thierry@arm.com>]

On 12/06/2019 09:16, Julien Thierry wrote:
> Hi Marc,
> 
> On 11/06/2019 18:03, Marc Zyngier wrote:

[...]

>> +
>> +void vgic_lpi_translation_cache_init(struct kvm *kvm)
>> +{
>> +	struct vgic_dist *dist = &kvm->arch.vgic;
>> +	unsigned int sz;
>> +	int i;
>> +
>> +	if (!list_empty(&dist->lpi_translation_cache))
>> +		return;
>> +
>> +	sz = atomic_read(&kvm->online_vcpus) * LPI_DEFAULT_PCPU_CACHE_SIZE;
>> +
>> +	for (i = 0; i < sz; i++) {
>> +		struct vgic_translation_cache_entry *cte;
>> +
>> +		/* An allocation failure is not fatal */
>> +		cte = kzalloc(sizeof(*cte), GFP_KERNEL);
>> +		if (WARN_ON(!cte))
>> +			break;
>> +
>> +		INIT_LIST_HEAD(&cte->entry);
>> +		list_add(&cte->entry, &dist->lpi_translation_cache);
> 
> Going through the series, it looks like this list is either empty
> (before the cache init) or has a fixed number
> (LPI_DEFAULT_PCPU_CACHE_SIZE * nr_cpus) of entries. And the list never
> grows nor shrinks throughout the series, so it seems odd to be using a
> list here.
> 
> Is there a reason for not using a dynamically allocated array instead of
> the list? (does list_move() provide a big perf advantage over swapping
> the data from one array entry to another? Or is there some other
> facility I am missing?
> 

Scratch that, I realized having the list makes it easier to implement
the LRU policy later in the series.

-- 
Julien Thierry

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