Re: [RFC PATCH for 4.15 09/14] Provide cpu_opv system call

----- On Oct 13, 2017, at 10:50 PM, Andi Kleen andi-Vw/NltI1exuRpAAqCnN02g@public.gmane.org wrote:

quoted

+	pagefault_disable();
+	switch (len) {
+	case 1:
+		if (__get_user(tmp._u8, (uint8_t __user *)p))
+			goto end;
+		tmp._u8 += (uint8_t)count;
+		if (__put_user(tmp._u8, (uint8_t __user *)p))
+			goto end;
+		break;

It seems the code size could be dramatically shrunk by using a function
pointer callback for the actual operation, and then avoiding all the
copies. Since this is only a fallback this shouldn't be a problem
(and modern branch predictors are fairly good in such situations anyways)

If you really want to keep the code it would be better if you used
some macros -- i bet there's a typo in here somewhere in this
forest.

Good point!

I'll add this in the next round. Meanwhile, here is the resulting
commit: https://github.com/compudj/linux-percpu-dev/commit/864b444f64f4c227ddc587d12631ff0d3440796c

Thanks,

Mathieu

-Andi

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com