This is very basic, for advanced users, but... it took me a while. So I explain it just in case somebody has the same problem as I. There's plenty of explanations everywhere, but I'm going to make it simple.

My computer (8 core Intel) was running really slow with GPU, I have other proyects running at the same time:
44,233.67 secs ACEMD2: GPU molecular dynamics v6.14 (cuda31)
100,153.34 secs ACEMD2: GPU molecular dynamics v6.15 (cuda31)

After googling everywhere, I understood that CPU was saturated, so I limited it to 7 cores (N-1):

cc_config.xml
<cc_config>
<options>
<ncpus>7</ncpus>
</options>
</cc_config>

<ncpus>N</ncpus>
Act as if there were N CPUs; i.e. to simulate 2 CPUs on a machine that has only 1. To use the number of available CPUs, set the value to -1 (was 0 which in newer clients really means zero to e.g. only allow GPU computing).

<ncpus> is not recommended. The suggested approach is to specify the % of processors to use in your preferences which achieves the same thing. When crunching GPUgrid work I set it to 87.5% which frees up a CPU core (on my 8 core machines). Much simpler and easier to change as needed than a cc_config file entry.

I run Boinc 6.12.34 on my home machine. Next to GPUGrid, I run WCG, because it seems pointless to waste cyclse on finding primes and hash and what not, but that is not the reason for this reply.

I have a Phenom II X4 (965 BE) with 4 cores and dedicate all CPU cycles to WCG and almost all GPU to GPUGrid. Since the recent discussion with the new WU's being dished out and keeping one CPU for that matter free, I would like to reduce the WCG use from 4 to 3 CPU's. I changed that in the WCG preferences for the home PC profile (use only 75%) but it still grabs all 4 cores.

What am I doing wrong?

I also tried to change it in the BOINC manager directly. That seemed to work. How can I tell that the free CPU is used to support the GPU now? Opening the task manager shows three cores at ~75%, one at ~50%.

I have a Phenom II X4 (965 BE) with 4 cores and dedicate all CPU cycles to WCG and almost all GPU to GPUGrid. Since the recent discussion with the new WU's being dished out and keeping one CPU for that matter free, I would like to reduce the WCG use from 4 to 3 CPU's. I changed that in the WCG preferences for the home PC profile (use only 75%) but it still grabs all 4 cores.

What am I doing wrong?

I also tried to change it in the BOINC manager directly. That seemed to work. How can I tell that the free CPU is used to support the GPU now? Opening the task manager shows three cores at ~75%, one at ~50%.

i have win7 on i7-950 , 12 Gb.
my boinc is on a secondary disk.

Try this :

boinc 7.0.20
latest nvidia certified drivers full reloaded with opencl 1.1

- my cc_config :

<cc_config>
<options>
<ncpus>-1</ncpus>
<report_results_immediately>1</report_results_immediately>
<use_all_gpus>1</use_all_gpus>
<save_stats_days>672</save_stats_days>
</options>
</cc_config>

- before stoping boinc, see in event report of boinc :
the free memory of your card and convert the x Mo in octet

i fixe <gpu_ram> for me to 603979776.0000 = 576 Mo << i have a 560 TI 560 : a litle more half , for one single wu.

- and add a new variable before relauching the boinc manager
SWAN_SYNC=0

- use nvida performance the increase the % fan to max (noisy) to cool the gpu
for my GPU 80% used -> %70 FAN at factory parameter : GPU is at 57° C

notice these are to be adapted for the possible number of wu :
<avg_ncpus>0.99</avg_ncpus>
<max_ncpus>0.99</max_ncpus>
<count>1</count>
for 1 single wu.
0.5 for 2 wu
0.33 for 3 wu
0.25 for 4 wu
depending of the gpu and gpu_ram needed for one task.

- my app_info.xml =

<app_info>

<app>
<name>acemdlong</name>
<user_friendly_name>Long runs (8-12 hours on fastest card)</user_friendly_name>
<non_cpu_intensive>0</non_cpu_intensive>
<download_url>http://www.ps3grid.net/PS3GRID/download/acemdlong_6.15_windows_intelx86__cuda31</download_url>
</app>

<file_info>
<name>acemdlong_6.15_windows_intelx86__cuda31</name>
<executable/>
</file_info>

<file_info>
<name>cudart32_31_9.dll</name>
<executable/>
</file_info>
<file_info>
<name>cufft32_31_9.dll</name>
<executable/>
</file_info>
<file_info>
<name>tcl85.dll</name>
<executable/>
</file_info>

<app_version>
<app_name>acemdlong</app_name>
<version_num>615</version_num>
<platform>windows_intelx86</platform>
<avg_ncpus>0.99</avg_ncpus>
<max_ncpus>0.99</max_ncpus>
<flops>197218977547.224270</flops>
<plan_class>cuda31</plan_class>
<api_version>7.0.20</api_version>
<coproc>
<type>CUDA</type>
<count>1</count>
</coproc>
<gpu_ram>805306368.000000</gpu_ram>
<file_ref>
<file_name>acemdlong_6.15_windows_intelx86__cuda31</file_name>
<main_program/>
</file_ref>
<file_ref>
<file_name>cudart32_31_9.dll</file_name>
<open_name>cudart32_31_9.dll</open_name>
<copy_file/>
</file_ref>
<file_ref>
<file_name>cufft32_31_9.dll</file_name>
<open_name>cufft32_31_9.dll</open_name>
<copy_file/>
</file_ref>
<file_ref>
<file_name>tcl85.dll</file_name>
<open_name>tcl85.dll</open_name>
<copy_file/>
</file_ref>
</app_version>


<app>
<name>acemdlong</name>
<user_friendly_name>Long runs (8-12 hours on fastest card)</user_friendly_name>
<non_cpu_intensive>0</non_cpu_intensive>
<download_url>http://www.ps3grid.net/PS3GRID/download/acemdlong_6.16_windows_intelx86__cuda31</download_url>
</app>

<file_info>
<name>acemdlong_6.16_windows_intelx86__cuda31</name>
<executable/>
</file_info>

<file_info>
<name>cudart32_31_9.dll</name>
<executable/>
</file_info>
<file_info>
<name>cufft32_31_9.dll</name>
<executable/>
</file_info>
<file_info>
<name>tcl85.dll</name>
<executable/>
</file_info>

<app_version>
<app_name>acemdlong</app_name>
<version_num>616</version_num>
<platform>windows_intelx86</platform>
<avg_ncpus>0.99</avg_ncpus>
<max_ncpus>0.99</max_ncpus>
<flops>197218977547.224270</flops>
<plan_class>cuda31</plan_class>
<api_version>7.0.20</api_version>
<coproc>
<type>CUDA</type>
<count>1</count>
</coproc>
<gpu_ram>805306368.000000</gpu_ram>
<file_ref>
<file_name>acemdlong_6.16_windows_intelx86__cuda31</file_name>
<main_program/>
</file_ref>
<file_ref>
<file_name>cudart32_31_9.dll</file_name>
<open_name>cudart32_31_9.dll</open_name>
<copy_file/>
</file_ref>
<file_ref>
<file_name>cufft32_31_9.dll</file_name>
<open_name>cufft32_31_9.dll</open_name>
<copy_file/>
</file_ref>
<file_ref>
<file_name>tcl85.dll</file_name>
<open_name>tcl85.dll</open_name>
<copy_file/>
</file_ref>
</app_version>


<app>
<name>acemd2</name>
<user_friendly_name>ACEMD2: GPU molecular dynamics</user_friendly_name>
<non_cpu_intensive>0</non_cpu_intensive>
<download_url>http://www.ps3grid.net/PS3GRID/download/acemd2_6.16_windows_intelx86__cuda31</download_url>
</app>

<file_info>
<name>acemd2_6.16_windows_intelx86__cuda31</name>
<executable/>
</file_info>

<app_version>
<app_name>acemd2</app_name>
<version_num>616</version_num>
<platform>windows_intelx86</platform>
<avg_ncpus>0.99</avg_ncpus>
<max_ncpus>0.99</max_ncpus>
<flops>60076679705.760513</flops>
<plan_class>cuda31</plan_class>
<api_version>7.0.20</api_version>
<coproc>
<type>CUDA</type>
<count>1</count>
</coproc>
<gpu_ram>603979776.000000</gpu_ram>
<file_ref>
<file_name>acemd2_6.16_windows_intelx86__cuda31</file_name>
<main_program/>
</file_ref>
<file_ref>
<file_name>tcl85.dll</file_name>
<open_name>tcl85.dll</open_name>
<copy_file/>
</file_ref>
<file_ref>
<file_name>cudart32_31_9.dll</file_name>
<open_name>cudart32_31_9.dll</open_name>
<copy_file/>
</file_ref>
<file_ref>
<file_name>cufft32_31_9.dll</file_name>
<open_name>cufft32_31_9.dll</open_name>
<copy_file/>
</file_ref>
</app_version>

</app_info>


- VErify préferences parameters.
100% CPU
100% of time of CPU,
-> min and max bufer : must be adapted to time of a wu, to avoid to be out of date.

A+
____________

Lest's say you have one GPU:
If you don't free your cores you will see 5 tasks = 4 task + 1 task for your GPU.
If you free one core you will see 4 task = 3 task + 1 task for your GPU.

Lest's say you have two GPUs:
If you don't free your cores you will see 6 tasks = 4 task + 2 task for your GPUs.
If you free one core you will see 5 task = 3 task + 2 task for your GPU.
If you free two cores you will see 4 task = 2 task + 2 task for your GPU.

When you change %CPU cores think that GPU usually takes 0,2-0,4 CPU but the CPU is not been use will make the CPUs task run faster.

<ncpus> is not recommended. The suggested approach is to specify the % of processors to use in your preferences which achieves the same thing. When crunching GPUgrid work I set it to 87.5% which frees up a CPU core (on my 8 core machines). Much simpler and easier to change as needed than a cc_config file entry.

Why? It should slow down all my task 87%, so I don't see it. I will test it.