20210430, 04:24  #12 
"Curtis"
Feb 2005
Riverside, CA
3×5×11×29 Posts 
If my only interest was using those two pieces of hardware to factors numbers as fast as possible, I'd run GNFS and ECM in parallel, with a queue of 23 numbers that survived ECM and are ready for GNFS (since a few in a row may succumb to ECM, leaving you starved for CPU work if you don't have a queue).
That would be *far* more than 0.32 depth! Then again, GPUECM still needs stage 2 to be done on one CPU core (right? that hasn't changed, has it?), so perhaps I'd let the GPU go idle sometimes. I'd also run really big curves if you're on C150s, I'd run about half a T45, then half a T50, then however many T55 curves would definitely finish in less time than the current GNFS job. Maybe half a T55? How far you get depends on how fast your GPU is; a 1060 obv isn't going to fly through as many curves as a 30xx. The idea is that your GPU can save you a couple of GNFS jobs you would have otherwise done if you'd stopped ECM at e.g. 2t45. In the context of "I am limited by my CPU", those are free factors! 
20210430, 04:50  #13 
Apr 2021
17 Posts 
Lots of great info, thanks!

20210430, 15:49  #14 
Sep 2009
2·1,021 Posts 
Given a GPU that can do stage 1 faster than the CPU can do stage 2 (after splitting the stage 2 runs over however many threads the CPU has) I'd treat stage 1 as nearly free and run ECM until (probable saving from the chance of finding a factor)/(CPU time needed for stage 2) matches CPU time needed to factor it with GNFS. Which probably won't be more than 23 digits above the optimum for CPU only since time increases quickly with target level.
In my case with 1 GPU and several CPUs I have to do a bit less than that so the GPU can pretest numbers fast enough to feed the CPUs. Chris 
20210430, 18:03  #15 
Apr 2021
17 Posts 
Thanks for that. That fits with my "back of the napkin number crunching" since B1 values and curve times seem directly proportional for time taken based on this https://mersenneforum.org/showpost.p...&postcount=59; so that might mean a few digits higher than 0.32x for GPU ECM even assuming best case scenario of 10x speed (which seems hit or miss itself). Maybe instead of 0.32x with CPU, 0.34x might be reasonable with GPU then.
Last fiddled with by Unitome on 20210430 at 18:14 
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