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POHuge performance hit for inlining sync method into async method
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  1. POHuge performance hit for inlining sync method into async method
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    copied!<p>I have a simple performance test, that indirectly calls <code>WriteAsync</code> many times. It performs reasonably as long as <code>WriteAsync</code> is implemented as shown below. However, when I inline <code>WriteByte</code> into <code>WriteAsync</code>, performance degrades by about factor 7.</p> <p>(To be clear: The <strong>only</strong> change that I make is replacing the statement containing the <code>WriteByte</code> call with the body of <code>WriteByte</code>.)</p> <p>Can anybody explain why this happens? I've had a look at the differences in the generated code with Reflector, but nothing struck me as so totally different as that it would explain the huge perf hit.</p> <pre><code>public sealed override async Task WriteAsync( byte[] buffer, int offset, int count, CancellationToken cancellationToken) { var writeBuffer = this.WriteBuffer; var pastEnd = offset + count; while ((offset &lt; pastEnd) &amp;&amp; ((writeBuffer.Count &lt; writeBuffer.Capacity) || await writeBuffer.FlushAsync(cancellationToken))) { offset = WriteByte(buffer, offset, writeBuffer); } this.TotalCount += count; } </code></pre> <pre><code>private int WriteByte(byte[] buffer, int offset, WriteBuffer writeBuffer) { var currentByte = buffer[offset]; if (this.previousWasEscapeByte) { this.previousWasEscapeByte = false; this.crc = Crc.AddCrcCcitt(this.crc, currentByte); currentByte = (byte)(currentByte ^ Frame.EscapeXor); ++offset; } else { if (currentByte &lt; Frame.InvalidStart) { this.crc = Crc.AddCrcCcitt(this.crc, currentByte); ++offset; } else { currentByte = Frame.EscapeByte; this.previousWasEscapeByte = true; } } writeBuffer[writeBuffer.Count++] = currentByte; return offset; } </code></pre>
 

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