powerpc/pseries: Fix cpu hotplug

Currently, pseries_cpu_die() calls msleep() while polling RTAS for
the status of the dying cpu.

However, if the cpu that is going down also happens to be the one
doing the tick then we're hosed as the tick_do_timer_cpu 'baton' is
only passed later on in tick_shutdown() when _cpu_down() does the
CPU_DEAD notification.  Therefore jiffies won't be updated anymore.

This replaces that msleep() with a cpu_relax() to make sure we're not
going to schedule at that point.

With this patch my test box survives a 100k iterations hotplug stress
test on _all_ cpus, whereas without it, it quickly dies after ~50
iterations.

Signed-off-by: Sebastien Dugue <sebastien.dugue@bull.net>
Cc: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>

diff --git a/arch/powerpc/platforms/pseries/hotplug-cpu.c b/arch/powerpc/platforms/pseries/hotplug-cpu.c
index 1f032483c026e613b4ab84649ab2f3562fb7c031..a20ead87153db18566a2034179a9041ea6cc456d 100644 (file)
--- a/arch/powerpc/platforms/pseries/hotplug-cpu.c
+++ b/arch/powerpc/platforms/pseries/hotplug-cpu.c
@@ -116,7 +116,7 @@ static void pseries_cpu_die(unsigned int cpu)
                cpu_status = query_cpu_stopped(pcpu);
                if (cpu_status == 0 || cpu_status == -1)
                        break;
-               msleep(200);
+               cpu_relax();
        }
        if (cpu_status != 0) {
                printk("Querying DEAD? cpu %i (%i) shows %i\n",