[julia-users] Re: Result changes if I change the number of workers
Are you doing floating point calculations? Some FP operations aren't associative and therefore may appear different on successive runs of a parallel operation depending on what's summed first: julia> (0.1 + 0.2) + 0.3 0.6001 julia> 0.1 + (0.2 + 0.3) 0.6 On Thursday, November 26, 2015 at 11:48:25 AM UTC-8, Eduardo Lenz wrote: > > Hi. > > I came across a very weird behaviour when using a very simple @parallel > loop. The block is quite large and complex, but the idea is the following: > > > A = zeros(some_dimension) > A = convert(SharedArray,A) > @sync @parallel for i=1:some_dimension > > Lots of code, but with no function calls > > A[i] += block_result > > end > > some computation with sdata(A). > > If I use 4 processes, I get one result. With 8 processes, a diferent > result. Without parallel processing, another one. > > I am probably losing something, but I think this is not the intended > behaviour. > > I am using jula 4.11, fedora 23 - 64 bits. > > Thanks for your help. >
[julia-users] Re: Result changes if I change the number of workers
Thanks Seth. I have a LOT of floating point calculations inside this loop. So, there should be it ! Now I have to figure it out how to overcome itif it is even possible :0) Thanks a lot !! On Thursday, November 26, 2015 at 5:59:56 PM UTC-2, Seth wrote: > > Are you doing floating point calculations? Some FP operations aren't > associative and therefore may appear different on successive runs of a > parallel operation depending on what's summed first: > > julia> (0.1 + 0.2) + 0.3 > 0.6001 > > > julia> 0.1 + (0.2 + 0.3) > 0.6 > > > On Thursday, November 26, 2015 at 11:48:25 AM UTC-8, Eduardo Lenz wrote: >> >> Hi. >> >> I came across a very weird behaviour when using a very simple @parallel >> loop. The block is quite large and complex, but the idea is the following: >> >> >> A = zeros(some_dimension) >> A = convert(SharedArray,A) >> @sync @parallel for i=1:some_dimension >> >> Lots of code, but with no function calls >> >> A[i] += block_result >> >> end >> >> some computation with sdata(A). >> >> If I use 4 processes, I get one result. With 8 processes, a diferent >> result. Without parallel processing, another one. >> >> I am probably losing something, but I think this is not the intended >> behaviour. >> >> I am using jula 4.11, fedora 23 - 64 bits. >> >> Thanks for your help. >> >
[julia-users] Re: Result changes if I change the number of workers
Do any of your calculations depend on the values of A? If so they will get different values depending in what order A[i] is updated. And the order depends on scheduling of the processes, which is not deterministic. Cheers Lex On Friday, November 27, 2015 at 8:44:42 AM UTC+10, Eduardo Lenz wrote: > > Thanks Seth. > > I have a LOT of floating point calculations inside this loop. So, there > should be it ! > > Now I have to figure it out how to overcome itif it is even possible > :0) > > Thanks a lot !! > > On Thursday, November 26, 2015 at 5:59:56 PM UTC-2, Seth wrote: >> >> Are you doing floating point calculations? Some FP operations aren't >> associative and therefore may appear different on successive runs of a >> parallel operation depending on what's summed first: >> >> julia> (0.1 + 0.2) + 0.3 >> 0.6001 >> >> >> julia> 0.1 + (0.2 + 0.3) >> 0.6 >> >> >> On Thursday, November 26, 2015 at 11:48:25 AM UTC-8, Eduardo Lenz wrote: >>> >>> Hi. >>> >>> I came across a very weird behaviour when using a very simple @parallel >>> loop. The block is quite large and complex, but the idea is the following: >>> >>> >>> A = zeros(some_dimension) >>> A = convert(SharedArray,A) >>> @sync @parallel for i=1:some_dimension >>> >>> Lots of code, but with no function calls >>> >>> A[i] += block_result >>> >>> end >>> >>> some computation with sdata(A). >>> >>> If I use 4 processes, I get one result. With 8 processes, a diferent >>> result. Without parallel processing, another one. >>> >>> I am probably losing something, but I think this is not the intended >>> behaviour. >>> >>> I am using jula 4.11, fedora 23 - 64 bits. >>> >>> Thanks for your help. >>> >>
