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

Message ID 20171010071109.31207-1-npiggin@gmail.com
State Not Applicable
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  • powerpc/pseries/cpuidle: add polling idle for shared processor guests
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Commit Message

Nicholas Piggin Oct. 10, 2017, 7:11 a.m.
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(-)

Comments

Nicholas Piggin Oct. 10, 2017, 9:42 a.m. | #1
On Tue, 10 Oct 2017 17:11:09 +1000
Nicholas Piggin <npiggin@gmail.com> 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
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Patch

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 },
 };