[PATCH] powerpc/pseries/cpuidle: add polling idle for shared processor guests

For shared processor guests (e.g., KVM), add an idle polling mode rather
than immediately returning to the hypervisor when the guest CPU goes
idle.

Test setup is a 2 socket POWER9 with 4 guests running, each with vCPUs
equal to 1/2 of real of CPUs. Saturated each guest with tbench. Using
polling idle gives about 1.4x throughput.

Kernel compile speed was not changed significantly.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 drivers/cpuidle/cpuidle-pseries.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/cpuidle/cpuidle-pseries.c b/drivers/cpuidle/cpuidle-pseries.c
index e9b3853d93ea..16be7ad30fe1 100644
--- a/drivers/cpuidle/cpuidle-pseries.c
+++ b/drivers/cpuidle/cpuidle-pseries.c

@@ -171,11 +171,17 @@ static struct cpuidle_state dedicated_states[] = {
  * States for shared partition case.
  */
 static struct cpuidle_state shared_states[] = {
+	{ /* Snooze */
+		.name = "snooze",
+		.desc = "snooze",
+		.exit_latency = 0,
+		.target_residency = 0,
+		.enter = &snooze_loop },
 	{ /* Shared Cede */
 		.name = "Shared Cede",
 		.desc = "Shared Cede",
-		.exit_latency = 0,
-		.target_residency = 0,
+		.exit_latency = 10,
+		.target_residency = 100,
 		.enter = &shared_cede_loop },
 };
 

-- 
2.13.3

On Tue, 10 Oct 2017 17:11:09 +1000
Nicholas Piggin [off-list ref] wrote:

For shared processor guests (e.g., KVM), add an idle polling mode rather
than immediately returning to the hypervisor when the guest CPU goes
idle.

Test setup is a 2 socket POWER9 with 4 guests running, each with vCPUs
equal to 1/2 of real of CPUs. Saturated each guest with tbench. Using
polling idle gives about 1.4x throughput.

Actually it's even more noticeable when the host is not over subscribed
by the looks. 2.5x-3x increase in throughput for just a single guest.

Thanks,
Nick

On Tue, 10 Oct 2017 17:11:09 +1000
Nicholas Piggin [off-list ref] wrote:

For shared processor guests (e.g., KVM), add an idle polling mode rather
than immediately returning to the hypervisor when the guest CPU goes
idle.

Test setup is a 2 socket POWER9 with 4 guests running, each with vCPUs
equal to 1/2 of real of CPUs. Saturated each guest with tbench. Using
polling idle gives about 1.4x throughput.

Kernel compile speed was not changed significantly.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>

What should we do about this one?

On Tue, 2017-10-10 at 07:11:09 UTC, Nicholas Piggin wrote:

For shared processor guests (e.g., KVM), add an idle polling mode rather
than immediately returning to the hypervisor when the guest CPU goes
idle.

Test setup is a 2 socket POWER9 with 4 guests running, each with vCPUs
equal to 1/2 of real of CPUs. Saturated each guest with tbench. Using
polling idle gives about 1.4x throughput.

Kernel compile speed was not changed significantly.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/f2ac428e0edabbca41b9dfe9473a90

cheers