[PATCH] [POWERPC] Fix thinko in cpu_thread_mask_to_cores()

[PATCH] [POWERPC] Fix thinko in cpu_thread_mask_to_cores()

[Benjamin Herrenschmidt]

The function cpu_thread_mask_to_cores() which returns a cpumask
of one and only one thread enabled for a given core has a bug
as it's shifting things in the wrong direction.

Note: The implementation is still sub-optimal in the sense that
for a given core, the thread set in the result may not be any of
the threads set in the input, which can lead to more IPIs then
strictly necessary, but it isn't incorrect per-se. I'll improve
that later.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
---

 include/asm-powerpc/cputhreads.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- linux-work.orig/include/asm-powerpc/cputhreads.h	2008-02-22 14:22:34.000000000 +1100
+++ linux-work/include/asm-powerpc/cputhreads.h	2008-02-22 14:22:39.000000000 +1100
@@ -35,7 +35,7 @@ static inline cpumask_t cpu_thread_mask_
 
 	res = CPU_MASK_NONE;
 	for (i = 0; i < NR_CPUS; i += threads_per_core) {
-		cpus_shift_right(tmp, threads_core_mask, i);
+		cpus_shift_left(tmp, threads_core_mask, i);
 		if (cpus_intersects(threads, tmp))
 			cpu_set(i, res);
 	}

Re: [PATCH] [POWERPC] Fix thinko in cpu_thread_mask_to_cores()

[Benjamin Herrenschmidt]

On Fri, 2008-02-22 at 14:26 +1100, Benjamin Herrenschmidt wrote:
> The function cpu_thread_mask_to_cores() which returns a cpumask
> of one and only one thread enabled for a given core has a bug
> as it's shifting things in the wrong direction.
> 
> Note: The implementation is still sub-optimal in the sense that
> for a given core, the thread set in the result may not be any of
> the threads set in the input, which can lead to more IPIs then
> strictly necessary, but it isn't incorrect per-se. I'll improve
> that later.
> 
> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> ---

Note that this function is, afaik, not used by anything in-tree at the 
moment, so the bug isn't hurting anybody, but I'd rather have it
fixed anyway.

Ben.