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Old 2008-11-13, 19:20   #1
Meikel
 
Nov 2008

916 Posts
Default How to assign helper threads affinity?

Hi!

Unfortunately it seems not possible to set the affinity of helper threads.

I've got a new Core i7, and currently the highest throughput can be achieved by starting 4 independent LL checks. I don't gain, nor loose anything, when starting 8 independent LL checks (some gain through hyperthreading, balanced by some loss through half the L2 cache i guess).

What I would like to do is this:
[Worker #1]
Affinity=0
HelperAffinity=1

(and so on).

Without this setting, the helper threads get assigned quite weirdly:
First worker says this:
Setting affinity to run worker on logical CPU #0
Setting affinity to run helper thread 1 on logical CPU #2

Second worker says this:
Setting affinity to run worker on logical CPU #2
Setting affinity to run helper thread 1 on logical CPU #4

And so on.

But hey, I notices something strange: The last worker says:
Setting affinity to run worker on logical CPU #6
Setting affinity to run helper thread 1 on logical CPU #8

OOOps? Do I have 9 (!) CPUs? Numbering from #0 to #8?
Or is there rather a bug in the output of the affinity of the helper thread?

Can you confirm this, George?

Does the "worker"-line number CPUs from #0 to #7, while the "helper"-line numbers them from #1 to #8?

Then the assignment algorithm would be fine, just the numbering is inconsistent :-)))

Edit: No, its really a wrong and weird assignment. The Task-Manager says, that with those 8 threads, the CPU is loaded only 50%! Cores 0 and 1 are at 50%, Cores 2, 4 and 6 are at 100%, while cores 3, 5 and 7 are totally empty!

Edit2: Activating "smart assignment" is even weirder: Workers 1 and 2 are BOTH given the same affinities:
Setting affinity to run worker on logical CPUs 0,4
Setting affinity to run helper thread 1 on logical CPUs 0,4

And Workers 3 and 4 do the same with CPUs 1,5.

Last fiddled with by Meikel on 2008-11-13 at 19:43
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Old 2008-11-14, 03:15   #2
starrynte
 
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Oct 2008
California

22·59 Posts
Default

i can confirm the weird output: i have a hyperthreaded p4, thus there are two logical cpu's. when i said main worker to cpu #0, it shows "setting affinity to run worker on cpu #0" and "setting affinity to run helper thread on cpu #2"
if i set main worker to run on cpu #1: "setting affinity to run worker on cpu #1" and "setting affinity to run helper thread on cpu #3" ...
given that it says "setting affinity to run worker on cpu #1" when i set main worker to run on cpu #1, i assume it should read cpu #0 and #1, or cpu #1 and #0, but i certainly don't have 4 cpus!
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Old 2008-11-14, 09:52   #3
Prime95
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Aug 2002
Yeehaw, FL

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I'll be looking into this when I get home in 3 days.
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Old 2008-11-22, 14:36   #4
Prime95
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Aug 2002
Yeehaw, FL

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Affinity code is being reworked. Please try again when 25.8 is available.
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