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WFE performance busy wait improvement #195

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WFE performance busy wait improvement #195

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2 changes: 1 addition & 1 deletion src/Emulator/Cores/tlib
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Submodule tlib updated 2 files
+11 −0 arch/arm/helper.c
+6 −0 arch/arm/op_helper.c
11 changes: 5 additions & 6 deletions src/Emulator/Peripherals/Peripherals/CPU/BaseCPU.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -792,14 +792,13 @@ protected CpuResult CpuThreadBodyInner(bool singleStep, bool skipThisRound = fal
this.Trace();
var instructionsToSkip = Math.Min(InstructionsToNearestLimit(), instructionsLeftThisRound);

virtualTimeAhead = machine.LocalTimeSource.ElapsedVirtualHostTimeDifference;
if(!machine.LocalTimeSource.AdvanceImmediately && virtualTimeAhead.Ticks > 0 && instructionsToSkip > 0)
if(!machine.LocalTimeSource.AdvanceImmediately && instructionsToSkip > 0)
{
// Don't fall behind realtime by sleeping
var intervalToSleep = TimeInterval.FromCPUCycles(instructionsToSkip, PerformanceInMips, out var cyclesResiduum).WithTicksMin(virtualTimeAhead.Ticks);
// Sleep for the full remaining quantum while waiting for an interrupt.
// sleeper.Interrupt() from OnGPIO will wake us early when an IRQ arrives,
// so we only burn host CPU for the actual wait duration, not the full quantum.
var intervalToSleep = TimeInterval.FromCPUCycles(instructionsToSkip, PerformanceInMips, out var cyclesResiduum);
sleeper.Sleep(intervalToSleep.ToTimeSpan(out var nsResiduum), out var intervalSlept);
// If we have a CPU of less than 10 MIPS, it might be the case that the interval slept (which is in units of 100 ns)
// is less than 1 instruction. Just round up it in this case.
instructionsToSkip = Math.Max(TimeInterval.FromTimeSpan(intervalSlept, nsResiduum).ToCPUCycles(PerformanceInMips, out var _) + cyclesResiduum, 1);
}

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