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Reduce contention in ClockCache #7338

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merged 1 commit into from
Aug 16, 2024
Merged

Reduce contention in ClockCache #7338

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12 changes: 9 additions & 3 deletions src/Nethermind/Nethermind.Core/Caching/ClockCache.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@
using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;

using Nethermind.Core.Threading;
Expand Down Expand Up @@ -74,7 +75,8 @@ private bool SetSlow(TKey key, TValue val)
return false;
}

int offset = _cacheMap.Count;
int offset = _count;
Debug.Assert(_cacheMap.Count == _count);
if (FreeOffsets.Count > 0)
{
offset = FreeOffsets.Dequeue();
Expand All @@ -86,14 +88,16 @@ private bool SetSlow(TKey key, TValue val)

_cacheMap[key] = new LruCacheItem(offset, val);
KeyToOffset[offset] = key;
_count++;
Debug.Assert(_cacheMap.Count == _count);

return true;
}

private int Replace(TKey key)
{
int position = Clock;
int max = _cacheMap.Count;
int max = _count;
while (true)
{
if (position >= max)
Expand All @@ -108,6 +112,7 @@ private int Replace(TKey key)
{
ThrowInvalidOperationException();
}
_count--;
break;
}

Expand All @@ -132,6 +137,7 @@ public bool Delete(TKey key)

if (_cacheMap.Remove(key, out LruCacheItem? ov))
{
_count--;
KeyToOffset[ov.Offset] = default;
ClearAccessed(ov.Offset);
FreeOffsets.Enqueue(ov.Offset);
Expand All @@ -157,7 +163,7 @@ public bool Contains(TKey key)
return _cacheMap.ContainsKey(key);
}

public int Count => _cacheMap.Count;
public int Count => _count;

private class LruCacheItem(int offset, TValue v)
{
Expand Down
3 changes: 3 additions & 0 deletions src/Nethermind/Nethermind.Core/Caching/ClockCacheBase.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,8 @@ public abstract class ClockCacheBase<TKey>
protected Queue<int> FreeOffsets { get; } = new();

protected int Clock { get; set; } = 0;
// Use local count to avoid lock contention with reads on ConcurrentDictionary.Count
protected int _count = 0;
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Why introduce _count here while it's touched only by descendant classes?


protected ClockCacheBase(int maxCapacity)
{
Expand All @@ -35,6 +37,7 @@ protected void Clear()
{
if (MaxCapacity == 0) return;

_count = 0;
Clock = 0;
FreeOffsets.Clear();
KeyToOffset.AsSpan().Clear();
Expand Down
12 changes: 9 additions & 3 deletions src/Nethermind/Nethermind.Core/Caching/ClockKeyCache.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@
using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;

using Nethermind.Core.Threading;
Expand Down Expand Up @@ -51,7 +52,8 @@ private bool SetSlow(TKey key)
return false;
}

offset = _cacheMap.Count;
offset = _count;
Debug.Assert(_cacheMap.Count == _count);
if (FreeOffsets.Count > 0)
{
offset = FreeOffsets.Dequeue();
Expand All @@ -63,14 +65,16 @@ private bool SetSlow(TKey key)

_cacheMap[key] = offset;
KeyToOffset[offset] = key;
_count++;
Debug.Assert(_cacheMap.Count == _count);

return true;
}

private int Replace(TKey key)
{
int position = Clock;
int max = _cacheMap.Count;
int max = _count;
while (true)
{
if (position >= max)
Expand All @@ -85,6 +89,7 @@ private int Replace(TKey key)
{
ThrowInvalidOperationException();
}
_count--;
break;
}

Expand All @@ -108,6 +113,7 @@ public bool Delete(TKey key)

if (_cacheMap.Remove(key, out int offset))
{
_count--;
ClearAccessed(offset);
FreeOffsets.Enqueue(offset);
return true;
Expand All @@ -131,5 +137,5 @@ public bool Contains(TKey key)
return _cacheMap.ContainsKey(key);
}

public int Count => _cacheMap.Count;
public int Count => _count;
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Suggested change
public int Count => _count;
public int Count => Volatile.Read(ref _count);

}