Preface for mfakto 0.15pre7
This is a developmental version of mfakto. It has been verified to produce correct results. However, performance has not been optimized and there may be bugs and incomplete features. Please help improve mfakto by doing tests, providing feedback and reporting issues. Of course, code contributions are always welcome too.
You can get support via the following means:
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Contents
0 What is mfakto? 1 Compilation 1.1 Linux 1.2.1 Windows: MSVC 1.2.2 Windows: MinGW 1.3 macOS 2 Running mfakto 2.1 Supported GPUs 2.2 Linux 2.3 Windows 2.4 macOS 3 Getting work and reporting results 4 Known issues 4.1 Non-issues 5 Tuning 6 FAQ 7 Plans
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mfakto is an OpenCL port of mfaktc that aims to have the same features and functions. mfaktc is a program that trial factors Mersenne numbers. It stands for "Mersenne faktorisation* with CUDA" and was written for Nvidia GPUs. Both programs are used primarily in the Great Internet Mersenne Prime Search.
Primality tests are computationally intensive, but we can save time by finding small factors. GPUs are very efficient at this task due to their parallel nature. Only one factor is needed to prove a number composite.
mfakto uses a modified Sieve of Eratosthenes to generate a list of possible factors for a given Mersenne number. It then uses modular exponentiation to test these factors. Although this step is only done on the GPU in practice, mfakto can perform both steps on either the CPU or GPU. You can find more details at the GIMPS website: https://mersenne.org/various/math.php#trial_factoring
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General requirements:
Please note: the AMD APP SDK has been discontinued. If you still want to use it to compile mfakto, make sure you have version 2.5 or later. You can download the SDK here: https://community.amd.com/thread/227948
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Requires:
Steps:
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Requires:
Steps:
download and install the OpenCL SDK from AMD: https://github.com/GPUOpen-LibrariesAndSDKs/OCL-SDK/releases
open mfaktoVS12.sln in Visual Studio. You can use any recent version as Visual Studio will automatically update your project settings. If the option does not appear, right-click the solution and select "Retarget solution" from the menu.
open the project properties and select the configuration and platform
go to C/C++ > General > Additional Include Directories and ensure it contains the path to the OpenCL headers:
$(OCL_ROOT)\include
now go to Linker > General > Additional Library Directories and ensure it contains the correct paths:
32 bits: $(OCL_ROOT)\lib\x86 64 bits: $(OCL_ROOT)\lib\x86_64
select Build > Build Solution to compile mfakto
Additional notes:
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Requires:
Initial steps:
MinGW can be optionally used with MSYS2 to compile mfakto:
install MSYS2 using the instructions at the home page: https://www.msys2.org
launch the MSYS2 shell and install the required packages:
pacman -S mingw-w64-x86_64-gcc make
start the 32-bit or 64-bit MinGW shell and navigate to the mfakto folder
cd src
make (cross your fingers)
Otherwise:
Additional notes:
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Requires:
Steps:
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General requirements:
macOS users do not need any additional software as OpenCL is already part of the system.
Open a terminal window and run 'mfakto -h' for possible parameters. You may also want to check mfakto.ini for additional settings. mfakto typically fetches work from worktodo.txt as specified in the INI file. See section 3 on how to obtain assignments and report results.
A typical worktodo.txt file looks like this: -- begin example -- Factor=[assignment ID],66362159,64,68 Factor=[assignment ID],3321932899,76,77 -- end example --
You can launch mfakto after getting assignments. In this case, mfakto should trial factor M66362159 from 64 to 68 bits, followed by M3321932899 from 76 to 77 bits.
mfakto has a built-in self-test that automatically optimizes parameters. Please run 'mfakto -st' each time you:
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AMD:
Other devices:
Intel HD Graphics 4000 and later. Currently not supported on macOS.
OpenCL-enabled CPUs via the '-d c' option. Currently fails
Nvidia devices. Supported but may fail on some hardware
without atomics, mfakto may not correctly process multiple factors found in the same class. It may report only one factor or even an incorrect one, the latter due to scrambled data from multiple factors. PrimeNet automatically rejects factors that do not divide a Mersenne number. If this happens, run the exponent and bit level again on the CPU or another device. You can run mfakto on the CPU using the '-d c' option or use Prime95 instead. Lowering GridSize in mfakto.ini can also reduce the chance of error.
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Requirements:
AMD Catalyst 11.4 or higher. Consider using at least 14.4 as some previous versions have a bug that causes high CPU loads.
AMD APP SDK 2.5 or higher for systems without Catalyst 11.10 or above. It is recommended to update your drivers as the SDK has been discontinued. If you still want to use it to run mfakto, make sure the path to the appropriate library folder is in the system Path variable:
32 bits: %AMDAPPSDKROOT%\lib\x86 64 bits: %AMDAPPSDKROOT%\lib\x86_64
you may also need the Microsoft Visual C++ 2010 Redistributable Package for your platform and language:
32 bits: https://microsoft.com/en-us/download/details.aspx?id=5555 64 bits: https://microsoft.com/en-us/download/details.aspx?id=14632
Steps:
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You must have a PrimeNet account to participate. Simply visit the GIMPS website at https://mersenne.org to create one. Once you've signed up, you can get assignments in several ways.
From the GIMPS website: Step 1) log in to the GIMPS website with your username and password Step 2) on the menu bar, select Manual Testing > Assignments Step 3) open the link to the manual GPU assignment request form Step 4) enter the number of assignments or GHz-days you want Step 5) click "Get Assignments"
Users with older GPUs may want to use the regular form.Using the GPU to 72 tool: GPU to 72 is a website that "subcontracts" assignments from the PrimeNet server. It was previously the only means to obtain work at high bit levels. Although the manual GPU assignment form now serves this purpose, GPU to 72 remains the more popular option.
GPU to 72 website: https://gpu72.comUsing the MISFIT tool: MISFIT is a Windows tool that automatically requests assignments and submits results. You can get it here: https://mersenneforum.org/misfit
From mersenne.ca: James Heinrich's website mersenne.ca offers assignments for exponents up to 32 bits. You can get such work here: https://mersenne.ca/tf1G
Be aware that mfakto currently does not work below 60 bits.Advanced usage: As mfakto works best on long-running jobs, you may want to manually extend your assignments. Let's assume you've received an assignment like this: Factor=[assignment ID],78467119,65,66
This means the PrimeNet server has assigned you to trial factor M78467119
from 65 to 66 bits. However, take a look at the factoring limits:
http://mersenne.org/various/math.php
According to the table, the exponent is factored to 71 bits before being
tested. Because mfakto runs very fast on modern GPUs, you might want to go
directly to 71 or even 72 bits. Simply edit the ending bit level before
starting mfakto. For example:
Factor=[assignment ID],78467119,65,72
It is important to submit the results once you're done. Do not report
partial results as the exponent may be reassigned to someone else in the
interim, resulting in duplicate work and wasted cycles.
Please do not manually extend assignments from GPU to 72 as users are
requested not to "trial factor past the level you've pledged."
Once you have your assignments, copy the "Factor=..." lines directly into
your worktodo.txt file. Start mfakto, sit back and let it do its job.
Running mfakto is also a great way to stress test your GPU. ;-)Submitting results: mfakto currently cannot communicate with the PrimeNet server, so you must manually submit the results. To prevent abuse, admin approval is required for manual submissions. You can request approval by contacting George Woltman at woltman@alum.mit.edu or posting on the GIMPS forum: https://mersenneforum.org/forumdisplay.php?f=38
Step 1) log in to the GIMPS website with your username and password
Step 2) on the menu bar, select Manual Testing > Results
Step 3) upload the results.txt file produced by mfakto. You may archive or
delete the file after it has been processed.
There are several tools that can automate this process. You can find a
complete list here:
https://mersenneforum.org/showpost.php?p=465293&postcount=24##################
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On some devices, such as the Radeon HD 7700 - 7900 series, mfakto may be very slow at full GPU load due to fewer registers being available to the kernels. It will warn about this during startup. Set VectorSize=2 in mfakto.ini and restart mfakto to resolve this.
The user interface has not been extensively tested against invalid inputs. Although there are some checks, they are not foolproof by any means.
Your GUI may lag while running mfakto. On some Windows systems, the OS may restart the driver or even throw a BSoD in severe cases. Try lowering GridSize or NumStreams in your mfakto.ini file. Smaller grids should have better responsiveness at a slight performance loss. Another option for Windows users is to increase the GPU processing time: https://support.microsoft.com/en-us/help/2665946
SievePrimesAdjust is not always optimal. Experiment to find the best SievePrimes value and set SievePrimesAdjust=0 in your mfakto.ini file.
GPU is not found, fallback to CPU This happens on Linux when there is no X server. It can also happen on Windows when the GPU is not the primary display adapter. Try running mfakto on the main display rather than remotely. If that fails, then your graphics driver may be too old. It's also possible that the first device is not an AMD GPU. In this case, use the -d switch to specify a different device number. You can run 'clinfo' to get a list of devices.
on devices that do not support atomic operations, mfakto may not correctly process multiple factors found in the same class. It may report only one factor or even an incorrect one, the latter due to scrambled data from multiple factors. If this happens, run the exponent and bit level again on the CPU or another device. You can tell mfakto to run on the CPU using the '-d c' option or use Prime95 instead. Lowering GridSize in mfakto.ini can also reduce the chance of error.
mfakto does not support Intel HD Graphics on macOS Due to buggy drivers shipped with macOS, mfakto presently does not work with Intel HD Graphics. Unless Apple fixes the issue, Intel integrated GPUs may not be supported in the foreseeable future.
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mfakto runs slower on small ranges. Usually it doesn't make much sense to run mfakto with an upper limit below 64 bits. mfakto is designed to find factors between 64 and 92 bits, and is best suited for long-running jobs.
mfakto can find factors outside the given range. This is because mfakto works on huge factor blocks, controlled by GridSize in the INI file. The default value GridSize=3 means mfakto runs up to 1048576 factor candidates at once, per class. So the last block of each class is filled with factor candidates above the upper limit. This is a huge overhead for small ranges but can be safely ignored for larger ranges. For example, the average overhead is 0.5% for a class with 100 blocks but only 0.05% for one with 1000 blocks.
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You can find additional settings in the mfakto.ini file. Read it carefully before making changes. ;-)
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Q: Does mfakto support multiple GPUs? A: Currently no, but you can use the -d option to start an instance on a specific device. Please also see the next question.
Q: Can I run multiple instances of mfakto on the same computer? A: Yes. In most cases, this is necessary to make full use of a GPU when sieving on the CPU. Otherwise, one instance should fully utilize a single GPU.
Q: What tasks should I assign to mfakto? A: The 73-bit Barrett kernel is currently the fastest and works for factors between 60 to 73 bits. Selecting tasks for this kernel will give best results. However, the 79-bit Barrett kernel is quite fast too.
Q: I modified something in the kernel files, but my changes are not picked up by mfakto. How come? A: mfakto tries to load the pre-compiled kernel files in version 0.14 and later. The INI file parameter UseBinfile defines the name of the file containing the pre-compiled kernels. You can force mfakto to recompile the kernels by deleting the file and restarting mfakto.
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