2 versus 1 thread benchmark.

[hutch--]

I am sorry if I am wearing anyone out but the idea of these multithread tests is to see if a speed increase can be achieved on a dual core processor using multiple threads. This test piece does two tests, the first uses 2 threads to alternately zero fill a memory bufer and them write data to the buffer while the other bufer is being zero filled again. The second test does the two operations sequentialy in a single thread without any thread overhead.

On my single core PIV the threaded version is about 5% slower which is predictable, what I need to find out is if there is a speed increase with a dual core processor using two alternate threads.

This is the timing on my dev box, a single core PIV.

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[attachment deleted by admin]

[BogdanOntanu]

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Dual Core - Intel Core2 Duo T7200 at 2Ghz
Multiple threads are not faster even with dual core CPU's

[hutch--]

Thanks Bogdan,

I wonder if there is a way to test if the two threads are running on seperate cores ? Somewhere vauely I remember there being API functions that gave you the capacity to pick which core was being used but I forget where i saw it.

[GregL]

Pentium D 940 (3.2 GHz)

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I can see it using both cores in Performance Monitor.

As far as the APIs, I don't know, without researching it.

[hutch--]

Thanks Greg,

Sad to say it looks like the idea is a flop, it would probably be interesting to find out why it is no faster if it is being processed by both cores but then its probaby not worth the effort bothering.

[sinsi]

Q6600 2.4GHz on XP Home SP2

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I wonder if there is a way to test if the two threads are running on seperate cores ? Somewhere vauely I remember there being API functions that gave you the capacity to pick which core was being used but I forget where i saw it.

SetThreadAffinityMask maybe?

[Rainstorm]

intel core2duo 2.66Ghz  -  1333mhz/4M

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[BasilYercin]

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i added
SetThreadAffinityMask in start_fill_thread in order to select a cpu for the thread

[c0d1f1ed]

Sad to say it looks like the idea is a flop, it would probably be interesting to find out why it is no faster if it is being processed by both cores but then its probaby not worth the effort bothering.

I think it's quite obvious that it's RAM bandwidth limited.

[thomas_remkus]

Do you think there might be a change if you set the affinity?

[daydreamer]

Hutch what about if you simultanously write to ram with one thread and to a ddraw vram surface with second thread?

[hutch--]

Magnus,

Its worth a try as the memory does not overlap and should use different paths as well. I think c0d1f1ed is correct that its a memory access/bandwidth issue in the test piece even though the two addresses should be far enough apart was slower on both a single processor and Core 2 Duos.

[Sean1337]

Two thread: 2106 ms
One thread: 2231 ms

this is on a quad core cpu.

two threads evidently seems to be faster for me.

[zooba]

By removing the second 'double-fill' operation from the two-thread timing and increasing the loop count to 16 I get about a 20% advantage for the two-thread fill. There's about 5-10% the other way when the original code is used.

To be honest, I can't figure that out. My guess would be that ResumeThread() is slow. It is not intended for use outside of a debugging context, so perhaps using waitable objects (an event, most likely) would provide some improvement.

Cheers,

Zooba :U