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>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --git a/drivers/cpuidle/cpuidle-pseries.c b/drivers/cpuidle/cpuidle-pseries.c
index 0f2b697cbb270815e98cacdf2fde734327f3c446..9e56bc411061fd573bf06b56acf8dc4e6235ecd8 100644 (file)
--- a/drivers/cpuidle/cpuidle-pseries.c
+++ b/drivers/cpuidle/cpuidle-pseries.c
@@ -174,11 +174,17 @@ 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 },
 };