Re: [PATCH v4 7/7] iommu/vt-d: introduce per-cpu caching to iova allocation

[David Woodhouse <dwmw2-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>]

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On Wed, 2016-04-20 at 11:34 +0300, Adam Morrison wrote:
> +static void init_iova_rcaches(struct iova_domain *iovad)
> +{
...
> +               for_each_possible_cpu(cpu) {
> +                       cpu_rcache = per_cpu_ptr(rcache->cpu_rcaches, cpu);
> +                       spin_lock_init(&cpu_rcache->lock);
> +                       cpu_rcache->loaded = iova_magazine_alloc(GFP_KERNEL);
> +                       cpu_rcache->prev = iova_magazine_alloc(GFP_KERNEL);
> +               }

Hm, is that allocation excessive? We allocate the magazines for every
*possible* CPU, even those which may never actually exist in the
system?

Does it make sense to do that allocation only the first time it's
actually used on a given CPU? And either way, some comment to the
effect of "it's OK for allocation failure to leave these as NULL
because...." (fill in your reasoning here) probably wants to be added
to the above snippet of code.

Now that you've made this an extension of the IOVA API rather than an
incompatible change, this patch probably also wants to be split out
into two — changing intel-iommu only in the second patch.


-- 
David Woodhouse                            Open Source Technology Centre
David.Woodhouse@intel.com                              Intel Corporation


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