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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
#pragma once
const unsigned int MinNsPerNormalizedYield = 37; // measured typically 37-46 on post-Skylake
const unsigned int NsPerOptimalMaxSpinIterationDuration = 272; // approx. 900 cycles, measured 281 on pre-Skylake, 263 on post-Skylake
extern unsigned int g_yieldsPerNormalizedYield;
extern unsigned int g_optimalMaxNormalizedYieldsPerSpinIteration;
void InitializeYieldProcessorNormalizedCrst();
void EnsureYieldProcessorNormalizedInitialized();
class YieldProcessorNormalizationInfo
{
private:
unsigned int yieldsPerNormalizedYield;
unsigned int optimalMaxNormalizedYieldsPerSpinIteration;
unsigned int optimalMaxYieldsPerSpinIteration;
public:
YieldProcessorNormalizationInfo()
: yieldsPerNormalizedYield(g_yieldsPerNormalizedYield),
optimalMaxNormalizedYieldsPerSpinIteration(g_optimalMaxNormalizedYieldsPerSpinIteration),
optimalMaxYieldsPerSpinIteration(yieldsPerNormalizedYield * optimalMaxNormalizedYieldsPerSpinIteration)
{
}
friend void YieldProcessorNormalized(const YieldProcessorNormalizationInfo &);
friend void YieldProcessorNormalized(const YieldProcessorNormalizationInfo &, unsigned int);
friend void YieldProcessorWithBackOffNormalized(const YieldProcessorNormalizationInfo &, unsigned int);
};
FORCEINLINE void YieldProcessorNormalized(const YieldProcessorNormalizationInfo &normalizationInfo)
{
LIMITED_METHOD_CONTRACT;
unsigned int n = normalizationInfo.yieldsPerNormalizedYield;
_ASSERTE(n != 0);
do
{
YieldProcessor();
} while (--n != 0);
}
FORCEINLINE void YieldProcessorNormalized(const YieldProcessorNormalizationInfo &normalizationInfo, unsigned int count)
{
LIMITED_METHOD_CONTRACT;
_ASSERTE(count != 0);
if (sizeof(SIZE_T) <= sizeof(unsigned int))
{
// On platforms with a small SIZE_T, prevent overflow on the multiply below. normalizationInfo.yieldsPerNormalizedYield
// is limited to MinNsPerNormalizedYield by InitializeYieldProcessorNormalized().
const unsigned int MaxCount = (unsigned int)SIZE_T_MAX / MinNsPerNormalizedYield;
if (count > MaxCount)
{
count = MaxCount;
}
}
SIZE_T n = (SIZE_T)count * normalizationInfo.yieldsPerNormalizedYield;
_ASSERTE(n != 0);
do
{
YieldProcessor();
} while (--n != 0);
}
FORCEINLINE void YieldProcessorWithBackOffNormalized(
const YieldProcessorNormalizationInfo &normalizationInfo,
unsigned int spinIteration)
{
LIMITED_METHOD_CONTRACT;
// normalizationInfo.optimalMaxNormalizedYieldsPerSpinIteration cannot exceed the value below based on calculations done in
// InitializeYieldProcessorNormalized()
const unsigned int MaxOptimalMaxNormalizedYieldsPerSpinIteration =
NsPerOptimalMaxSpinIterationDuration * 3 / (MinNsPerNormalizedYield * 2) + 1;
_ASSERTE(normalizationInfo.optimalMaxNormalizedYieldsPerSpinIteration <= MaxOptimalMaxNormalizedYieldsPerSpinIteration);
// This shift value should be adjusted based on the asserted condition below
const UINT8 MaxShift = 3;
static_assert_no_msg(((unsigned int)1 << (MaxShift + 1)) >= MaxOptimalMaxNormalizedYieldsPerSpinIteration);
unsigned int n;
if (spinIteration <= MaxShift &&
((unsigned int)1 << spinIteration) < normalizationInfo.optimalMaxNormalizedYieldsPerSpinIteration)
{
n = ((unsigned int)1 << spinIteration) * normalizationInfo.yieldsPerNormalizedYield;
}
else
{
n = normalizationInfo.optimalMaxYieldsPerSpinIteration;
}
_ASSERTE(n != 0);
do
{
YieldProcessor();
} while (--n != 0);
}
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