why can't I run CPU and GPU miners at same time without problems?

[Ian Moone]

I am a total Noob at Mining bitcoins , well at anything Bitcoin.
my problem is that I have a server with 2 cpus and at this time it only has a single gpu, when ever I run the GPU I get an average of 178/Mhash/s ( not sure if thaT is any good) but when I run both GPU and CPU miners my GPU drops way down to between 1-5/Mhash/s why is that am I doing something wrong?

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[Gabi]

Nothing wrong, just the CPU miner use the CPU that, being busy, can't feed the GPU the data to make GPU miner work

So, GPU miner mhash happily drop.

Solution? Leave a free core for the GPU miner. Are they multi-core CPU? If for example you have a quadcore you can use 3 core for cpu mining and leave the fourth one idle, so the GPU miner will have a free core able to feed him

Sure, the fourth core will always be at like 0-1% of activity, but well, as you noticed, if you use it for CPU mining, it simply can't feed the GPU

[k0rsakoff]

Thank you, I was wondering why this wasn't working well for me either.

[Gabi]

I use BOINC and having a quadcore i give 3 cores to BOINC and leave one free for mining. Otherwise the same problem happens

Of course 1 core is enough to feed every GPU you have, even if you have 8 GPU 1 core is more than enough

[Ian Moone]

Ok I am running 2 8 core Opterons now for a what might seem like a silly question, How do I make one core open so tha tmy GPU can use that core? I currently am using windows7x64, and will most likely be switching to Linux very soon so I will need to know how to do this in Linux

[Gabi]

You simply leave a core free. Nothing more to do. Just leave a core free, if you have 8 core then tell the CPU miner to use 7 cores. If you run BOINC, well, same, tell it to use 7 cores.

[Ian Moone]

You simply leave a core free. Nothing more to do. Just leave a core free, if you have 8 core then tell the CPU miner to use 7 cores. If you run BOINC, well, same, tell it to use 7 cores.

That doesn't work for me , I tried to run just 12 cores for the CPU miner ( out of 16) but my GPU mine still drops all the way down to 1-5/Mhash/s

[DeathAndTaxes]

Are you sure you really have 16 cores.  Not 8 cores which appear as 16 due to hyperthreading enables on the OS?

What CPU specifically?

[Ian Moone]

I am running 2 Opteron 6128 cpu's tha tare 8 cores each .
ANyways I finally figured out how to set the CPU affinity in windows by just using the Process Explorer task manager and then scrolling down to poclbm.exe right clicking then choosing  "Set Affinity" . I had two of these one is for my GPU and the other was for my CPUs so once I figured out which one was the CPU I unchecked the 0 affinity and this solved my problem.
Thank you every one for your posts

[jade087]

If you're trying to both GPU and CPU mine at the same time on Windows, not only will you want to keep one core free for GPU mining, you'll want to set the CPU miner to affinity of the other cores. For example:

start /low /affinity 0x0e minerd.exe --threads 3 ...

I have a four-core machine, so I create three threads, and affinity is set to cores 2, 3, 4 (i.e. 0x02 | 0x04 | 0x08 = 0x0e). You might also want to set the affinity of the GPU miner to the first core in a similar fashion.

By restricting GPU mining to core 1, and CPU mining to cores 2 and 3, I can get both 250 MH/s for BTC and 8.5 kH/s for LTC...