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Old 2015-12-16, 17:14   #1
airsquirrels
 
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Default Mfakto cl_barret15_73_gs_2 - Not A Factor?

Mfakto cl_barret15_73_gs_2 kernel on Mfakto

Working on the very last remaining 47M exponent.

processing: TF factor 2742459209866315019473 for M47079733 (271-272)
Error code: 45, error text: 2742459209866315019473 is not a factor of M47079733

Retried on two different Fury Xs in different machines, both indicated this factor which primenet rejects.

Wolfram alpha says the remainder is 2742459209866315019471 (2 off from even)

Re-ran this on mfaktc on one GPU of a Titan Z:

no factor for M47079733 from 2^71 to 2^72 [mfaktc 0.21 barrett76_mul32_gs]
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Old 2015-12-16, 17:27   #2
kladner
 
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I saw this error only when I had a PSU going crazy. I assume that mfakto would behave similarly to mfaktc in this regard. The "normal" response of mfaktc, for me, if the card is too OC'd or the voltage is too low, is to crash. Not a Factor has been a very rare error for me.

EDIT: I am ignorant of CL Lucas, except for what I read here, so the causes might be different from CUDA.

Last fiddled with by kladner on 2015-12-16 at 17:29
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Old 2015-12-16, 18:22   #3
Mark Rose
 
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I TF'ed it on a GTX 760, for giggles:

no factor for M47079733 from 2^71 to 2^72 [mfaktc 0.21 barrett76_mul32_gs]
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Old 2015-12-16, 22:45   #4
VictordeHolland
 
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I'll run it on my HD7950
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Old 2015-12-16, 23:05   #5
science_man_88
 
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Code:
(19:03) gp > (1<<47079733+1)/2742459209866315019473
%68 = 24138552060634017262794635021044514699753531753848
(19:03) gp > floor(%)===%
%69 = 1
edit:the full result is cut off. I also tested it earlier through PARI and the way TF is done on mersennes.

Code:
(13:27) gp > a=binary(47079733);f=2742459209866315019473;b=Mod(1,f);for(x=1,#a,b=b^2;if(a[x]==1,b*=2));b-1
%57 = Mod(2742459209866315019471, 2742459209866315019473)

Last fiddled with by science_man_88 on 2015-12-16 at 23:14
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Old 2015-12-17, 00:43   #6
VictordeHolland
 
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We might be on to a bug in mfakto, my HD7950 also reports the factor:
AMD Catalyst 15.7
Windows 7 64bit

Code:
Runtime options
  Inifile                   mfakto.ini
  Verbosity                 1
  SieveOnGPU                yes
  MoreClasses               yes
  GPUSievePrimes            82486
  GPUSieveProcessSize       24Ki bits
  GPUSieveSize              96Mi bits
  FlushInterval             8
  WorkFile                  worktodo.txt
  ResultsFile               results.txt
  Checkpoints               enabled
  CheckpointDelay           300s
  Stages                    enabled
  StopAfterFactor           bitlevel
  PrintMode                 compact
  V5UserID                  VictordeHollander
  ComputerID                PCVICTOR
  TimeStampInResults        yes
  VectorSize                2
  GPUType                   GCN
  SmallExp                  no
  UseBinfile                mfakto_Kernels.elf
Compiletime options
Select device - Get device info - Loading binary kernel file mfakto_Kernels.elf
Compiling kernels.

OpenCL device info
  name                      Tahiti (Advanced Micro Devices, Inc.)
  device (driver) version   OpenCL 1.2 AMD-APP (1800.8) (1800.8 (VM))
  maximum threads per block 256
  maximum threads per grid  16777216
  number of multiprocessors 28 (1792 compute elements)
  clock rate                900MHz

Automatic parameters
  threads per grid          256
  optimizing kernels for    GCN

Started a simple selftest ...
Selftest statistics
  number of tests           108
  successful tests          108

selftest PASSED!
Code:
M47079733 has a factor: 2742459209866315019473 [TF:71:72:mfakto 0.14-Win cl_barrett15_73_gs_2]

((2^47079733-1) mod 2742459209866315019473
= 2742459209866315019471
That is indeed 2 off as people earlier mentioned. Could it be a precision problem with the barrett15_73 ?

Last fiddled with by VictordeHolland on 2015-12-17 at 01:05
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Old 2015-12-17, 00:56   #7
Gordon
 
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Quote:
Originally Posted by VictordeHolland View Post
We might be on to a bug in mfakto, my HD7950 also reports the factor:
AMD Catalyst 15.7
Windows 7 64bit

Code:
Runtime options
  Inifile                   mfakto.ini
  Verbosity                 1
  SieveOnGPU                yes
  MoreClasses               yes
  GPUSievePrimes            82486
  GPUSieveProcessSize       24Ki bits
  GPUSieveSize              96Mi bits
  FlushInterval             8
  WorkFile                  worktodo.txt
  ResultsFile               results.txt
  Checkpoints               enabled
  CheckpointDelay           300s
  Stages                    enabled
  StopAfterFactor           bitlevel
  PrintMode                 compact
  V5UserID                  VictordeHollander
  ComputerID                PCVICTOR
  TimeStampInResults        yes
  VectorSize                2
  GPUType                   GCN
  SmallExp                  no
  UseBinfile                mfakto_Kernels.elf
Compiletime options
Select device - Get device info - Loading binary kernel file mfakto_Kernels.elf
Compiling kernels.

OpenCL device info
  name                      Tahiti (Advanced Micro Devices, Inc.)
  device (driver) version   OpenCL 1.2 AMD-APP (1800.8) (1800.8 (VM))
  maximum threads per block 256
  maximum threads per grid  16777216
  number of multiprocessors 28 (1792 compute elements)
  clock rate                900MHz

Automatic parameters
  threads per grid          256
  optimizing kernels for    GCN

Started a simple selftest ...
Selftest statistics
  number of tests           108
  successful tests          108

selftest PASSED!
Code:
M47079733 has a factor: 2742459209866315019473 [TF:71:72:mfakto 0.14-Win cl_barrett15_73_gs_2]
Oh dear, if that's true.

But doesn't Primenet test the factors reported when you check them in?
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Old 2015-12-17, 01:07   #8
kladner
 
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Quote:
Originally Posted by Gordon View Post
Oh dear, if that's true.

But doesn't Primenet test the factors reported when you check them in?
Yes. It does. I was immediately informed that these factors were spurious when I checked them in. The form they reported in was not typical, either, and lines may have been repeated. I might even have the results.txt for them.....

As I said, in this case, my PSU had pretty much lost regulation. I did a lot of adjusting before , it sunk in that Something was Seriously Wrong. Swapping out the PSU fixed things.
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Old 2015-12-17, 14:22   #9
LaurV
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Well sir, you may have run in a very rare bug... My HD7970 finds the fake factor too.

Code:
mfakto 0.15pre2-Win (64bit build)

Runtime options
  Inifile                   mfakto.ini
  Verbosity                 2
  SieveOnGPU                yes
  MoreClasses               yes
  GPUSievePrimes            120000
  GPUSieveProcessSize       16Ki bits
  GPUSieveSize              64Mi bits
  FlushInterval             0
  WorkFile                  worktodo.txt
  ResultsFile               results.txt
  Checkpoints               enabled
  CheckpointDelay           1800s
  Stages                    enabled
  StopAfterFactor           class
  PrintMode                 compact
  V5UserID                  none
  ComputerID                none
  ProgressHeader            "Date    Time | class   Pct |   time     ETA | GHz-d/day    Sieve     Wait"
  ProgressFormat            "%d %T | %C %p%% | %t  %e |   %g  %s  %W%%"
  TimeStampInResults        yes
  VectorSize                2
  GPUType                   AUTO
  SmallExp                  yes
  UseBinfile                mfakto_Kernels.elf
Compiletime options

Select device - Get device info:
Device 1/1: Tahiti (Advanced Micro Devices, Inc.),
device version: OpenCL 1.2 AMD-APP (1084.4), driver version: 1084.4 (VM)
Extensions: cl_khr_fp64 cl_amd_fp64 cl_khr_global_int32_base_atomics cl_khr_global_int32_e
xtended_atomics cl_khr_local_int32_base_atomics cl_khr_local_int32_extended_atomics cl_khr
_int64_base_atomics cl_khr_int64_extended_atomics cl_khr_3d_image_writes cl_khr_byte_addre
ssable_store cl_khr_gl_sharing cl_ext_atomic_counters_32 cl_amd_device_attribute_query cl_
amd_vec3 cl_amd_printf cl_amd_media_ops cl_amd_media_ops2 cl_amd_popcnt cl_khr_d3d10_shari
ng cl_amd_c1x_atomics
Global memory:2147483648, Global memory cache: 16384, local memory: 32768, workgroup size:
 256, Work dimensions: 3[256, 256, 256, 0, 0] , Max clock speed:1050, compute units:32

OpenCL device info
  name                      Tahiti (Advanced Micro Devices, Inc.)
  device (driver) version   OpenCL 1.2 AMD-APP (1084.4) (1084.4 (VM))
  maximum threads per block 256
  maximum threads per grid  16777216
  number of multiprocessors 32 (2048 compute elements)
  clock rate                1050MHz

Automatic parameters
  threads per grid          256
  optimizing kernels for    GCN

Loading binary kernel file mfakto_Kernels.elf
Compiling kernels (build options: "-I. -DVECTOR_SIZE=2 -DGCN -O3 -DMORE_CLASSES -DCL_GPU_S
IEVE -DSMALL_EXP").
Started a simple selftest ...
Selftest statistics
  number of tests           130
  successful tests          130

selftest PASSED!

got assignment: exp=47079733 bit_min=71 bit_max=72 (10.16 GHz-days)
Starting trial factoring M47079733 from 2^71 to 2^72 (10.16GHz-days)
  k_min = 25076429823060 - k_max = 50152859648435
Using GPU kernel "cl_barrett15_73_gs_2"
No checkpoint file "M47079733.ckp" found.
Date    Time | class   Pct |   time     ETA | GHz-d/day    Sieve     Wait
Dec 17 19:21 | 4452  96.7% |  2.215   1m11s |    412.76   120373    0.00%
M47079733 has a factor: 2742459209866315019473

found 1 factor for M47079733 from 2^71 to 2^72 (partially tested) [mfakto 0.15pre2-Win cl_barrett15_73_gs_2]
tf(): total time spent: 33m 54.032s (431.50 GHz-days / day)
OTOH, false positive is not big deal, they are verified and hyper-verified. A false negative would be much worse, because that would mean three times wasting the time and the resources: once to do effectively the TF which missed the factor, twice to do the LL, because if the factor was missed, you would need to LL it, and last, third time, to DC it.

So, Bdot, are you there? Are we losing factors?

Last fiddled with by LaurV on 2015-12-17 at 14:31
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Old 2015-12-17, 15:16   #10
Mark Rose
 
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Quote:
Originally Posted by LaurV View Post
Are we losing factors?
We could look at the success rates for mfakto and see if it's lower than mfaktc.

Also, if the bug is found we should really spend time figuring out how likely it is that other factors were missed, and which they might be -- it might be worth spending time redoing certain classes of work.
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Old 2015-12-17, 15:43   #11
airsquirrels
 
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I'm away right now, but someone could try with the mfakto.ini set to use a different GCN optimization / kernel.

I now believe I have had this happen one other time but at the time did not think much of it. I can try to find that entry in my old logs.

The positive side is it found a factor of 2^p+1, which I believe I read somewhere in the factoring math that the algorithm could find those factors but the were trivial to check for. Perhaps that's what science man was saying?

I have the kernel source open, might try stepping through it at that k value to look for rounding errors/loss of precision.
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