Re: 2.6.16 - sys_sched_getaffinity & hotplug

[Paul Jackson]

Jack wrote:
> Should the following change be made to sched_getaffinity(). 
> 
> Index: linux/kernel/sched.c
> ===================================================================
> --- linux.orig/kernel/sched.c	2006-01-25 08:50:21.401747695 -0600
> +++ linux/kernel/sched.c	2006-01-27 16:57:24.504871895 -0600
> @@ -4031,7 +4031,7 @@ long sched_getaffinity(pid_t pid, cpumas
>  		goto out_unlock;
>  
>  	retval = 0;
> -	cpus_and(*mask, p->cpus_allowed, cpu_possible_map);
> +	cpus_and(*mask, p->cpus_allowed, cpu_online_map);

Adding Robert Love to the cc list, as he is Mr. sched_getaffinity,
I believe.

I ended up doing a similar change, to the cpus (and mems) masks
in the root (all encompassing) cpuset.  These now show the values
of cpu_online_map and node_online_map, not *_MASK_ALL.

My hunches are:
 * This change to cpu_online_map is a good one.
 * The man page sentence "Usually, all bits in the mask are set."
   might have meant something when it was written, but it is not
   now clear what.

-- 
                  I won't rest till it's the best ...
                  Programmer, Linux Scalability
                  Paul Jackson <pj@xxxxxxx> 1.925.600.0401
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