From 3dce49af0ecc67f243fdd37fbcfa3321f7d2047b Mon Sep 17 00:00:00 2001
From: Pawel Dziepak <pdziepak@quarnos.org>
Date: Fri, 17 Jan 2014 01:43:41 +0100
Subject: [PATCH] scheduler: Cache quantum length

---
 .../kernel/scheduler/scheduler_thread.cpp     | 36 ++++++++++---------
 .../kernel/scheduler/scheduler_thread.h       |  3 +-
 2 files changed, 21 insertions(+), 18 deletions(-)

diff --git a/src/system/kernel/scheduler/scheduler_thread.cpp b/src/system/kernel/scheduler/scheduler_thread.cpp
index 29d3ae2975..8651c5cacc 100644
--- a/src/system/kernel/scheduler/scheduler_thread.cpp
+++ b/src/system/kernel/scheduler/scheduler_thread.cpp
@@ -11,6 +11,9 @@ using namespace Scheduler;
 
 static bigtime_t sQuantumLengths[THREAD_MAX_SET_PRIORITY + 1];
 
+const int32 kMaximumQuantumLengthsCount	= 20;
+static bigtime_t sMaximumQuantumLengths[kMaximumQuantumLengthsCount];
+
 
 void
 ThreadData::_InitBase()
@@ -18,6 +21,7 @@ ThreadData::_InitBase()
 	fPriorityPenalty = 0;
 	fAdditionalPenalty = 0;
 	fEffectivePriority = GetPriority();
+	fBaseQuantum = sQuantumLengths[GetEffectivePriority()];
 	fCPUBound = false;
 
 	fTimeUsed = 0;
@@ -83,15 +87,6 @@ ThreadData::_ChooseCPU(CoreEntry* core, bool& rescheduleNeeded) const
 }
 
 
-inline bigtime_t
-ThreadData::_GetBaseQuantum() const
-{
-	SCHEDULER_ENTER_FUNCTION();
-
-	return sQuantumLengths[GetEffectivePriority()];
-}
-
-
 ThreadData::ThreadData(Thread* thread)
 	:
 	fThread(thread)
@@ -190,19 +185,16 @@ ThreadData::ComputeQuantum() const
 {
 	SCHEDULER_ENTER_FUNCTION();
 
-	bigtime_t quantum = _GetBaseQuantum();
 	if (IsRealTime())
-		return quantum;
+		return fBaseQuantum;
 
 	int32 threadCount = fCore->ThreadCount();
 	if (fCore->CPUCount() > 0)
 		threadCount /= fCore->CPUCount();
-	if (threadCount >= 1) {
-		quantum
-			= std::min(gCurrentMode->maximum_latency / threadCount, quantum);
-		quantum = std::max(quantum,	gCurrentMode->minimal_quantum);
-	}
 
+	bigtime_t quantum = fBaseQuantum;
+	if (threadCount < kMaximumQuantumLengthsCount)
+		quantum = std::min(sMaximumQuantumLengths[threadCount], quantum);
 	return quantum;
 }
 
@@ -232,6 +224,16 @@ ThreadData::ComputeQuantumLengths()
 		sQuantumLengths[priority] = _ScaleQuantum(kQuantum2, kQuantum1,
 			B_NORMAL_PRIORITY, B_IDLE_PRIORITY, priority);
 	}
+
+	for (int32 threadCount = 0; threadCount < kMaximumQuantumLengthsCount;
+		threadCount++) {
+
+		bigtime_t quantum = gCurrentMode->maximum_latency;
+		if (threadCount != 0)
+			quantum /= threadCount;
+		quantum = std::max(quantum, gCurrentMode->minimal_quantum);
+		sMaximumQuantumLengths[threadCount] = quantum;
+	}
 }
 
 
@@ -276,6 +278,8 @@ ThreadData::_ComputeEffectivePriority() const
 		ASSERT(fEffectivePriority < B_FIRST_REAL_TIME_PRIORITY);
 		ASSERT(fEffectivePriority >= B_LOWEST_ACTIVE_PRIORITY);
 	}
+
+	fBaseQuantum = sQuantumLengths[GetEffectivePriority()];
 }
 
 
diff --git a/src/system/kernel/scheduler/scheduler_thread.h b/src/system/kernel/scheduler/scheduler_thread.h
index bfcaa59e77..980d6c2fff 100644
--- a/src/system/kernel/scheduler/scheduler_thread.h
+++ b/src/system/kernel/scheduler/scheduler_thread.h
@@ -29,8 +29,6 @@ private:
 	inline	CPUEntry*	_ChooseCPU(CoreEntry* core,
 							bool& rescheduleNeeded) const;
 
-	inline	bigtime_t	_GetBaseQuantum() const;
-
 public:
 						ThreadData(Thread* thread);
 
@@ -121,6 +119,7 @@ private:
 			int32		fAdditionalPenalty;
 
 	mutable	int32		fEffectivePriority;
+	mutable	bigtime_t	fBaseQuantum;
 
 			bigtime_t	fTimeUsed;