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SubjectRe: [PATCH 06/10] x86: reduce memory and stack usage in intel_cacheinfo

* Mike Travis <travis@sgi.com> wrote:

> * Change the following static arrays sized by NR_CPUS to
> per_cpu data variables:
>
> _cpuid4_info *cpuid4_info[NR_CPUS];
> _index_kobject *index_kobject[NR_CPUS];
> kobject * cache_kobject[NR_CPUS];
>
> * Remove the local NR_CPUS array with a kmalloc'd region in
> show_shared_cpu_map().

thanks Travis, i've applied this to x86.git.

one observation:

> static ssize_t show_shared_cpu_map(struct _cpuid4_info *this_leaf, char *buf)
> {
> - char mask_str[NR_CPUS];
> - cpumask_scnprintf(mask_str, NR_CPUS, this_leaf->shared_cpu_map);
> - return sprintf(buf, "%s\n", mask_str);
> + int n = 0;
> + int len = cpumask_scnprintf_len(nr_cpu_ids);
> + char *mask_str = kmalloc(len, GFP_KERNEL);
> +
> + if (mask_str) {
> + cpumask_scnprintf(mask_str, len, this_leaf->shared_cpu_map);
> + n = sprintf(buf, "%s\n", mask_str);
> + kfree(mask_str);
> + }
> + return n;

the other changes look good, but this one looks a bit ugly and complex.
We basically want to sprintf shared_cpu_map into 'buf', but we do that
by first allocating a temporary buffer, print a string into it, then
print that string into another buffer ...

this very much smells like an API bug in cpumask_scnprintf() - why dont
you create a cpumask_scnprintf_ptr() API that takes a pointer to a
cpumask? Then this change would become a trivial and much more readable:

- char mask_str[NR_CPUS];
- cpumask_scnprintf(mask_str, NR_CPUS, this_leaf->shared_cpu_map);
- return sprintf(buf, "%s\n", mask_str);
+ return cpumask_scnprintf_ptr(buf, NR_CPUS, &this_leaf->shared_cpu_map);

Ingo


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