2.6.16 - sys_sched_getaffinity & hotplug
From: Jack Steiner
Date: Fri Jan 27 2006 - 18:05:46 EST
It appears if CONFIG_HOTPLUG_CPU is enabled, then all possible
cpus (0 .. NR_CPUS-1) are set in the cpu_possible_map on IA64.
void __init
smp_build_cpu_map (void)
{
...
for (cpu = 0; cpu < NR_CPUS; cpu++) {
ia64_cpu_to_sapicid[cpu] = -1;
#ifdef CONFIG_HOTPLUG_CPU <<<<
cpu_set(cpu, cpu_possible_map); <<<<
#endif <<<<
}
sched_getaffinity() returns the cpu_possible_map and'd with the current
task p->cpus_allowed. The default cpus_allowed is all ones.
This is causing problems for apps that use sched_get_sched_affinity()
to determine which cpus that they are allowed to run on.
The call to sched_getaffinity returns:
(from strace on a 2 cpu system with NR_CPUS = 512)
sched_getaffinity(0, 1024, { ffffffffffffffff, ffffff ...
The man page for sched_getaffinity() is ambiguous. It says:
- A set bit corresponds to a legally schedulable CPU
But it also says:
- Usually, all bits in the mask are set.
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);
out_unlock:
read_unlock(&tasklist_lock);
--
Thanks
Jack Steiner (steiner@xxxxxxx)
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/