I have a much better return when running WOO units with "t -2" on my i3 Skylake than with "t -4" on my i7 Skylake. With the latter, I have a gain of about 10% (shorter elapsed time) but with twice the cores being used.

Have others noticed something similar? I am tempted to have two units running on my i7 6700k with the "t -2" parm in lieu of "t -4".

Sounds like a case of ram bandwidth limiting. What is the ram speed and channels on the i3 and i7? i3 are practically not limited even with cheap ram, but when you double the cores without much faster ram, that can be a limit fast. I find dual channel dual rank 3200 ram on my 6700k at 4.0 GHz is close to being unlimited.

By all means try 2x2t but I wouldn't expect it to be much different than 1x4t. For big units like this, I'd not expect much difference in overall throughput between 4x1t and 1x4t, and I'd still prefer 1x4t just to keep unit times down.

Edit:

Here's a post I did on another forum while testing 7800X, but I also have my main system 6700k data in there. Note the 6700k has two flat lines - no significant difference between 1x4t and 4x1t unless you're running smaller FFT where there is some reduction with 4t. I'm not sure I understand the Skylake-X results yet, there is something going on with the new cache structure.

2133 ram speed is going to choke the 6700k. Do let us know the results for 2x2t but I wouldn't expect i3 speeds out of it.

The RAM in both machines is dual channel 2666 MHz but the mobo is limited to 2166 MHz. Since I am processing extra units so as to force the badge flip rather than wait for completed units to verify, there is no great urgency on my part to crunch WOO and, as a result, I will revert back to "t -2" so as to have two work units crunching simultaneously with the expectation that I will emulate my i3's performance.

I'd change the other two 4's to 2's also. Restart should do it, I've done so in past... is it boinc indicating 4 cores in use, or do you actually see 4 in use in task manager? The former would be down to that config, the latter isn't expected. Worst case, do a reboot to ensure things are reset.

By the way, I changed the app_config file to the following, powered down BM and restarted it but the single unit is still running with all 4 CPU's:

<app>
<name>llrWOO</name>
<max_concurrent>1</max_concurrent>
<fraction_done_exact>1</fraction_done_exact>
</app>
<app_version>
<app_name>llrWOO</app_name>
<cmdline>-t 2</cmdline>
<avg_ncpus>4</avg_ncpus>
<max_ncpus>4</max_ncpus>
</app_version>

Have I screwed up somewhere or must the current unit complete before the "-t 2" takes effect?

You might have to play with the CPU usage in boinc settings to get it to run the desired number of simultaneous units. This isn't great...

Change <max_ncpus>4</max_ncpus> back to 4 and it should run 2 Woodall WUs (or any other sub project) on 2 threads each. That sets the max number of TOTAL cores to use. So 2WUs with 2t each = 4 cores needed to run the same sub project simultaneously.
When you got the Cullen WU it has it's own settings (if Woodal and Cullen both have <max_ncpus>2</max_ncpus> set to 2 than that's a TOTAL of 4) and is probably why it's working now (running 2 WUs at 2t each), but to run 2 of the same sub project you need to do the above.
____________
Largest Primes to Date:
As Double Checker: SR5 109208*5^1816285+1 Dgts-1,269,534
As Initial Finder: SR5 243944*5^1258576-1 Dgts-879,713

<max_concurrent>1</max_concurrent>

This is why WOO is only running 1 at a time.

<app>
<name>llrWOO</name>
<fraction_done_exact/>
</app>
<app_version>
<app_name>llrWOO</app_name>
<cmdline>-t 2</cmdline>
<avg_ncpus>2</avg_ncpus>
<max_ncpus>4</max_ncpus>
</app_version>

The <max_concurrent>1</max_concurrent> could also limit the number of each sub project WUs you can run simultaneously.

Exactly my point.

in Message 109570 (7th post in this thread) Anthony posted his app_config for WOO and said it was only running one unit. The rest of the thread was trying to fix that, ending with him switching to CUL and thinking everything was ok. However, next time he runs WOO it's still only going to run one unit at a time.

He needs to change WOO's max_concurrent value to 2 in his app_config.

I'd change the other two 4's to 2's also. Restart should do it, I've done so in past... is it boinc indicating 4 cores in use, or do you actually see 4 in use in task manager? The former would be down to that config, the latter isn't expected. Worst case, do a reboot to ensure things are reset.