Bitcoin Forum

Greetings,
Heard about Bitcoin on Security Now podcast and was curious what this was all about.

I average about 25Mhash/s. When I run two miners, my rate is about half for each.
Is there any reason why I should be running two miners vs 1? Do the probability of finding a block improve at all?

On a second laptop, I am experimenting with the solo mode ( i average 5Mhash/s). I could leave it on 24/7 but would it be worth it?

After running for couple of hours @ 25Mhash/s on Slush's pool, i have about 0.07BTC



I am using GUIMiner with
username.miner1
username.miner2
on Nvidia Quadro FX 3700M GPU  and Windows 7 64bit.

thank you

edit:
cleaned up my post.
I have been reading more forum posts now, looks like even at Ghash/s, its getting increasingly difficult to find a block.
 ???

That kind of M/hash generation, its not worth the power, to power your pc's.  Get a powerful ATI video card... 5xxx or 6xxx series, or don't bother with mining IMO.

you can mine at two pools, if one goes down, resources are taken by the 2nd miner but...

unlike cpu miner, gpu miner does not distribute speed evenly, not sure for cuda miner, you can check :)

Running multiple GPU miners on one GPU will cause the GPU to be shared between processes, and thus results in context switches. Context switches take some time so your total performance will suffer.

There's no theoretical benefit from running two miners on the same GPU if the total hashing rate is the same. If the total rate was higher when running two then that would indicate that the single miner wasn't totally utilizing your GPU, which could be addressed by increasing the aggression of the miner. As long as you're running with an aggression level above 1 or 2 I expect a single miner would max out your Quadro.

GUIMiner author here, good to see the miner is working for you.

I run two miners on the same GPU so if one pool goes down the other will pick up the slack. By adjusting the -f flag value you can control which one is the "primary" and which is the "backup". I have my primary as -f40 and my backup as -f60. In general a higher f value is a lower priority.

There is in fact benefit in doing that. Context switch overhead is nothing compared to kernel launch and buffer copy one. You are likely to utilize the GPU better. With faster GPUs that makes sense. Also, with NVidia Fermi architecture, concurrent kernel execution is possible which does not bring 2x faster speeds of course but utilizes the GPU resources even better (speedup about 5-10%). That's why I create 2 threads per device in hashkill, each of them with its own context and queue. Speedup is not significant, but still there is one. You can easily check speed difference if you run it with -G 1 (single thread) and -G 2 (two threads per GPU). With my 6870, it's about 3 M/s.

However, for a multithreaded application, this requires a thread-safe OpenCL implementation. Thread-safety is a requirement to OpenCL 1.1 standart which is implemented in SDK 2.3 and above. So with 2.2 and 2.1 your only way is with multiple processes, not multiple threads. In this case, yes, context switches are more expensive.