9. Which is fastest?
var ints = new int[InnerLoop];
var random = new Random();
for (var inner = 0; inner < InnerLoop; ++inner)
{
ints[inner] = random.Next();
}
// ------------------------------------------------
var ints = new int[InnerLoop];
var random = new Random();
Parallel.For(
0,
InnerLoop,
i => ints[i] = random.Next()
);
10. SHARED STATE Race condition
var ints = new int[InnerLoop];
var random = new Random();
for (var inner = 0; inner < InnerLoop; ++inner)
{
ints[inner] = random.Next();
}
// ------------------------------------------------
var ints = new int[InnerLoop];
var random = new Random();
Parallel.For(
0,
InnerLoop,
i => ints[i] = random.Next()
);
11. SHARED STATE Poor performance
var ints = new int[InnerLoop];
var random = new Random();
for (var inner = 0; inner < InnerLoop; ++inner)
{
ints[inner] = random.Next();
}
// ------------------------------------------------
var ints = new int[InnerLoop];
var random = new Random();
Parallel.For(
0,
InnerLoop,
i => ints[i] = random.Next()
);
12.
13. Then and now
Metric VAX-11/750 (’80) Today Improvement
MHz 6 3300 550x
Memory MB 2 16384 8192x
Memory MB/s 13 R ~10000
W ~2500
770x
190x
14. Then and now
Metric VAX-11/750 (’80) Today Improvement
MHz 6 3300 550x
Memory MB 2 16384 8192x
Memory MB/s 13 R ~10000
W ~2500
770x
190x
Memory nsec 225 70 3x
15. Then and now
Metric VAX-11/750 (’80) Today Improvement
MHz 6 3300 550x
Memory MB 2 16384 8192x
Memory MB/s 13 R ~10000
W ~2500
770x
190x
Memory nsec 225 70 3x
Memory cycles 1.4 210 -150x
26. Solution 1 – Locks
var ints = new int[InnerLoop];
var random = new Random();
Parallel.For(
0,
InnerLoop,
i => {lock (ints) {ints[i] = random.Next();}}
);
27. Solution 2 – No sharing
var ints = new int[InnerLoop];
Parallel.For(
0,
InnerLoop,
() => new Random(),
(i, pls, random) =>
{ints[i] = random.Next(); return random;},
random => {}
);
29. Solution 3 – Less overhead
var ints = new int[InnerLoop];
Parallel.For(
0,
InnerLoop / Modulus,
() => new Random(),
(i, pls, random) =>
{
var begin = i * Modulus ;
var end = begin + Modulus ;
for (var iter = begin; iter < end; ++iter)
{
ints[iter] = random.Next();
}
return random;
},
random => {}
);
30. var ints = new int[InnerLoop];
var random = new Random();
for (var inner = 0; inner < InnerLoop; ++inner)
{
ints[inner] = random.Next();
}
31. Solution 4 – Independent runs
var tasks = Enumerable.Range (0, 8).Select (
i => Task.Factory.StartNew (
() =>
{
var ints = new int[InnerLoop];
var random = new Random ();
while (counter.CountDown ())
{
for (var inner = 0; inner < InnerLoop; ++inner)
{
ints[inner] = random.Next();
}
}
},
TaskCreationOptions.LongRunning))
.ToArray ();
Task.WaitAll (tasks);
