linux-kernel - [PATCH 1/2] cpuidle : auto-promotion for cpuidle states

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Message-Id: <20190322062530.7586-2-huntbag@linux.vnet.ibm.com>
Date:   Fri, 22 Mar 2019 01:25:29 -0500
From:   Abhishek Goel <huntbag@...ux.vnet.ibm.com>
To:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-pm@...r.kernel.org
Cc:     rjw@...ysocki.net, daniel.lezcano@...aro.org, mpe@...erman.id.au,
        Abhishek Goel <huntbag@...ux.vnet.ibm.com>
Subject: [PATCH 1/2] cpuidle : auto-promotion for cpuidle states

Currently, the cpuidle governors (menu /ladder) determine what idle state
an idling CPU should enter into based on heuristics that depend on the
idle history on that CPU. Given that no predictive heuristic is perfect,
there are cases where the governor predicts a shallow idle state, hoping
that the CPU will be busy soon. However, if no new workload is scheduled
on that CPU in the near future, the CPU will end up in the shallow state.

In case of POWER, this is problematic, when the predicted state in the
aforementioned scenario is a lite stop state, as such lite states will
inhibit SMT folding, thereby depriving the other threads in the core from
using the core resources.

To address this, such lite states need to be autopromoted. The cpuidle-
core can queue timer to correspond with the residency value of the next
available state. Thus leading to auto-promotion to a deeper idle state as
soon as possible.

Signed-off-by: Abhishek Goel <huntbag@...ux.vnet.ibm.com>
---
 drivers/cpuidle/cpuidle.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index 2406e2655..c4d1c1b38 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c
@@ -584,11 +584,8 @@ static void __cpuidle_unregister_device(struct cpuidle_device *dev)

 static void __cpuidle_device_init(struct cpuidle_device *dev)
 {
-	int i;
 	memset(dev->states_usage, 0, sizeof(dev->states_usage));
 	dev->last_residency = 0;
-	for (i = 0; i < CPUIDLE_STATE_MAX; i++)
-               dev->states_usage[i].disable = true;
 }

 /**
-- 
2.17.1