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LAN_403

Andy

Thu Nov 28 2013, 12:19AM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

Yep.
Is there any way to speed up code like this?

for(l1=0;l1<largenumber;l1++) {
for(l2=0;l2<largenumber;l2++) {
for(l3=0;l3<largenumber;l3++) {

do stuff
}
}
}

I've got four cores, but if I get more, there will be more for loops.

Thanks

Carbon_Rod

Thu Nov 28 2013, 04:07AM

Registered Member #65 Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155

Not sure why you nested the loops instead of an abstraction for a dynamic programming solution.
And, there is still an instantiation like cost when going parallel.

Andy

Thu Nov 28 2013, 06:49AM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

Did you mean ?
for(l1=0;l1<largenumber;l1++) {
for(l2=i1+1;l2<largenumber;l2++) {
for(l3=l2+1;l3<largenumber;l3++) {

do stuff
}
}
}

Wastrel

Thu Nov 28 2013, 03:29PM

Registered Member #4095 Joined: Thu Sept 15 2011, 03:19PM
Location: England.
Posts: 122

GPUs have a very small amount of memory per computational unit and have big penalties for conditional and branched code. In the case of your loops, optimising depends mostly on what 'stuff' actually is.

It sounds like you are trying to bruteforce a problem instead of solving it. Can you tell us any more?

Andy

Thu Nov 28 2013, 07:03PM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

I'm not sure how to workout the numbers apart from bruteforce, the below just checks to see if the the combinations when mixed with water can occupier the space

Thanks

unsigned int atoms[85];

atoms[0] = 100000;
for(i=1;i<85;i++) {
atoms[i]=atoms[0]/i;
}

H2O = atoms[7]+(atoms[0]*2);

for(l1=0;l1<largenumber; l1++) {
for(l2=i1+1;l2<largenumber;l2++) {
for(l3=l2+1;l3<largenumber;l3++) {

test = atoms[l]+atoms[l1]+atoms[l2];
test = test + H2O
if(test == 100000 || test == 200000 || test == 300000) {
fprintf(out,"%s%s%s",atomsname[l],atomsname[l1] ,atomsname[l2]);
}
someother test based on numbers

}
}
}

Wastrel

Fri Nov 29 2013, 03:01PM

Registered Member #4095 Joined: Thu Sept 15 2011, 03:19PM
Location: England.
Posts: 122

The code is currently a bit broken and I'm assuming the actual table is more complicated for real atoms. It is important to get the method working first, then optimise the algorithm and lastly optimise the code.

In the case of this algorithm the first two tests fail automatically because they are less than the value for water on it's own. The goal value, 300000 would best be represented by a variable set to 300000-H2O which pushes code out
of the inner loop (and out of all of them, but this is where it costs the most).

If the real values for atom[x] are a progressive sequence then the inner loop can be replaced by a binary search tree, which would speed up the code by about ten times. If the real values for atom[x] are not in a progressive sequence, then reorder them. The absolute representation of the atoms is not important to the code.

Andy

Mon Dec 02 2013, 06:42AM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

Thanks Wastrel
I have to run the bruteforce code more than once, I've saved the combinations to hdd, and will load it in ram, what I understood from the binary search tree, split the combinations into 5 files and can select the part to bruteforce with a check.

@Shrad
Checked out a blade server 24cores 64gig of ram and 2* 1tb hdd for $340 month,

Shrad

Mon Dec 02 2013, 08:40AM

Registered Member #3215 Joined: Sun Sept 19 2010, 08:42PM
Location:
Posts: 780

yup, that's the kind of machines you would use for pure CPU taskforce

you have to use a unix server distro to take full advantage of it through some paralleling libraries

if you have multiple less-capable scavenged servers you also have the opportunity to cluster them, there are specialized distros but that's another story

Andy

Mon Dec 02 2013, 04:59PM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

I installed zorin 64bit and have been running from that.

"you would have to add some RAM or you will eat through read/write cycles of your SD card pretty quickly"

I think I fried my second hdd, the program now comes up with Bus error(core dumped) :( , what do you think could be wrong, or is it fixable

Shrad

Mon Dec 02 2013, 09:57PM

Registered Member #3215 Joined: Sun Sept 19 2010, 08:42PM
Location:
Posts: 780

it occurs only with flash memory.. as it has a limited read/write count before a memory cell is dead, if you use some small files which are updated really fast in permanent use, you'll eat the cells pretty fast..

the same will occur with mechanical devices but it will be from mechanical use/abuse

the solution is to create a small ramdisk (something like 4Gb) and make all your file access from there, so you also gain in speed (by a factor of 100 sometimes)

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