linux-kernel - [RFC PATCH v1 04/11] sched/idle: make the fast idle path for short idle periods

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Date:   Mon, 10 Jul 2017 09:38:34 +0800
From:   Aubrey Li <aubrey.li@...el.com>
To:     tglx@...utronix.de, peterz@...radead.org, len.brown@...el.com,
        rjw@...ysocki.net, ak@...ux.intel.com, tim.c.chen@...ux.intel.com,
        arjan@...ux.intel.com, paulmck@...ux.vnet.ibm.com,
        yang.zhang.wz@...il.com
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Aubrey Li <aubrey.li@...ux.intel.com>
Subject: [RFC PATCH v1 04/11] sched/idle: make the fast idle path for short idle periods

From: Aubrey Li <aubrey.li@...ux.intel.com>

The system will enter a fast idle loop if the predicted idle period
is shorter than the threshold.
---
 kernel/sched/idle.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index cf6c11f..16a766c 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -280,6 +280,8 @@ static void cpuidle_generic(void)
  */
 static void do_idle(void)
 {
+	unsigned int predicted_idle_us;
+	unsigned int short_idle_threshold = jiffies_to_usecs(1) / 2;
 	/*
 	 * If the arch has a polling bit, we maintain an invariant:
 	 *
@@ -291,7 +293,12 @@ static void do_idle(void)
 
 	__current_set_polling();
 
-	cpuidle_generic();
+	predicted_idle_us = cpuidle_predict();
+
+	if (likely(predicted_idle_us < short_idle_threshold))
+		cpuidle_fast();
+	else
+		cpuidle_generic();
 
 	__current_clr_polling();
 
-- 
2.7.4