path: root/arch/powerpc/platforms/pseries/setup.c
diff options
authorAnton Blanchard <anton@samba.org>2010-05-16 20:02:39 +0000
committerBenjamin Herrenschmidt <benh@kernel.crashing.org>2010-05-21 17:31:12 +1000
commitb878dc00595440586874952dd85ce9b803360b87 (patch)
tree172832984c2ca6661cb48899c40b5734cdfa82a3 /arch/powerpc/platforms/pseries/setup.c
parentdd04c63c96425af9b6741f3abf0ad25d6b1c0e8d (diff)
powerpc: Use smt_snooze_delay=-1 to always busy loop
Right now if we want to busy loop and not give up any time to the hypervisor we put a very large value into smt_snooze_delay. This is sometimes useful when running a single partition and you want to avoid any latencies due to the hypervisor or CPU power state transitions. While this works, it's a bit ugly - how big a number is enough now we have NO_HZ and can be idle for a very long time. The patch below makes smt_snooze_delay signed, and a negative value means loop forever: echo -1 > /sys/devices/system/cpu/cpu0/smt_snooze_delay This change shouldn't affect the existing userspace tools (eg ppc64_cpu), but I'm cc-ing Nathan just to be sure. Signed-off-by: Anton Blanchard <anton@samba.org> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Diffstat (limited to 'arch/powerpc/platforms/pseries/setup.c')
1 files changed, 5 insertions, 5 deletions
diff --git a/arch/powerpc/platforms/pseries/setup.c b/arch/powerpc/platforms/pseries/setup.c
index 6710761bf60..a6d19e3a505 100644
--- a/arch/powerpc/platforms/pseries/setup.c
+++ b/arch/powerpc/platforms/pseries/setup.c
@@ -496,13 +496,14 @@ static int __init pSeries_probe(void)
-DECLARE_PER_CPU(unsigned long, smt_snooze_delay);
+DECLARE_PER_CPU(long, smt_snooze_delay);
static void pseries_dedicated_idle_sleep(void)
unsigned int cpu = smp_processor_id();
unsigned long start_snooze;
unsigned long in_purr, out_purr;
+ long snooze = __get_cpu_var(smt_snooze_delay);
* Indicate to the HV that we are idle. Now would be
@@ -517,13 +518,12 @@ static void pseries_dedicated_idle_sleep(void)
* has been checked recently. If we should poll for a little
* while, do so.
- if (__get_cpu_var(smt_snooze_delay)) {
- start_snooze = get_tb() +
- __get_cpu_var(smt_snooze_delay) * tb_ticks_per_usec;
+ if (snooze) {
+ start_snooze = get_tb() + snooze * tb_ticks_per_usec;
- while (get_tb() < start_snooze) {
+ while ((snooze < 0) || (get_tb() < start_snooze)) {
if (need_resched() || cpu_is_offline(cpu))
goto out;