posted May 17, 2011, 1:51 PM by Victor Zakharov
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updated May 17, 2011, 2:13 PM
]
I recently had a Microsoft workshop session and became excited about parallel for/foreach/etc. There we got a solid 60% of efficiency. It means that whenever number of cores increases by 2x, performance is boosted by 1.6x. I became curious about it, and created a test project to verify the fact for myself. Here are the results I got on subsequent runs (time in milliseconds + efficiency):
    I even got 96% on some early build, which did not show that information clearly (hence, no screenshot).
Two points from here: 1. Yes, performance is better on multi-core machines, exactly as expected. 2. No, it does not have 100% efficiency, and is in fact very dependent on Windows, with efficiency ranging from 27% to 96%. It appears to be no way to predict efficiency factor at any given moment, so don't rely on it too much.
For reference, I am running on a Core 2 Duo E7200 @ 2.53 GHz, which has Windows performance rating of 6.1. And this is the code (VB.NET console application, using framework 4.0):
Module Module1
Const UBOUND As Integer = 100000000
Public Sub AAA(n As Integer)
Dim i As Integer = (n / 2)
End Sub
Sub Main()
Dim st1 As New Stopwatch
st1.Start()
For n = 1 To UBOUND
AAA(n)
Next
st1.Stop()
Dim st2 As New Stopwatch
st2.Start()
System.Threading.Tasks.Parallel.For(1, UBOUND, AddressOf AAA)
st2.Stop()
MsgBox("Single threaded: " & st1.ElapsedMilliseconds & vbNewLine &
"Multi-threaded: " & st2.ElapsedMilliseconds & vbNewLine &
"Efficiency: " & Format((st1.ElapsedMilliseconds / st2.ElapsedMilliseconds - 1) * 100, "N") & " %")
End Sub
End Module
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