On 09/13/2016 03:52 PM, Luck, Tony wrote:
> On Tue, Sep 13, 2016 at 03:40:18PM -0700, Dave Hansen wrote:
>> Are you sure you don't want to add RDT to disabled-features.h? You have
>> a config option for it, so it seems like you should also be able to
>> optimize some of these checks away when the config option is off.
>
> Makefile looks like this:
>
> obj-$(CONFIG_INTEL_RDT) += intel_rdt.o intel_rdt_rdtgroup.o
> intel_rdt_schemata.o
>
> which seems to skip compiling all our code when the CONFIG
> option is off.
>
> Our hooks to generic code look like:
>
> +#ifdef CONFIG_INTEL_RDT
> +extern void rdtgroup_fork(struct task_struct *child);
> +extern void rdtgroup_exit(struct task_struct *tsk);
> +#else
> +static inline void rdtgroup_fork(struct task_struct *child) {}
> +static inline void rdtgroup_exit(struct task_struct *tsk) {}
> +#endif /* CONFIG_INTEL_RDT */
>
> Does this disabled-features.h thing do something more?
If you have cpuid checks in common code, disabled-features.h can compile
them out if the config options are turned off. For instance:
if (cpu_feature_enabled(X86_FEATURE_PKU))
foo();
is equivalent to:
#ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS
if (boot_cpu_has(X86_FEATURE_PKU))
foo();
#endif
But, if all the cpu_has(c, X86_FEATURE_CAT_L3) checks are confined to
files only compiled under CONFIG_INTEL_RDT then it won't do you much
good. But, it's pretty simple to add things, and would help you out if
checks spread beyond intel_rdt*.c.
