Re: [RFC][PATCH] x86, fpu: dynamically allocate 'struct fpu'

Ingo Molnar
2015-07-17T08:45:35Z

* Dave Hansen <dave@sr71.net> wrote:

> >> #endif /* _ASM_X86_FPU_H */
> >> diff -puN arch/x86/kernel/process.c~dynamically-allocate-struct-fpu arch/x86/kernel/process.c
> >> --- a/arch/x86/kernel/process.c~dynamically-allocate-struct-fpu 2015-07-16 10:50:42.360571875 -0700
> >> +++ b/arch/x86/kernel/process.c 2015-07-16 12:00:59.204808551 -0700
> >> @@ -81,7 +81,7 @@ EXPORT_SYMBOL_GPL(idle_notifier_unregist
> >> */
> >> int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
> >> {
> >> - *dst = *src;
> >> + memcpy(dst, src, arch_task_struct_size());
> >
> > This is actually vaguely performance-critical, which makes me thing
> > that using some kind of inline or other real way (config macro, ifdef,
> > etc) to detect whether there's an arch override would be better than a
> > weak function.
>
> Fair enough. I'll send out another version in a bit if there are no more
> comments.

Beyond making it a build time switch for other architectures, I'd also suggest
introducing a __read_mostly task_struct_size variable on x86, so that we can
write:

memcpy(dst, src, task_struct_size);

Thanks,

Ingo